Pandas 0.25.2 causes regressions in eland testsuite

[Winterflower]

In order to support Python 3.8, we will need to upgrade eland 's Pandas dependency to 0.25.2 from the current 0.25.1.
Keeping the dependency as 0.25.1 and using eland with Python 3.8 causes the following test failure

======================================================================================= FAILURES ========================================================================================
_________________________________________________________________________ TestDataFrameQuery.test_simple_query __________________________________________________________________________
self = <eland.tests.dataframe.test_query_pytest.TestDataFrameQuery object at 0x7febc580af70>
    def test_simple_query(self):
        ed_flights = self.ed_flights()
        pd_flights = self.pd_flights()
>       assert pd_flights.query('FlightDelayMin > 60').shape == \
               ed_flights.query('FlightDelayMin > 60').shape
eland/tests/dataframe/test_query_pytest.py:50: 


self = <pandas.core.computation.expr.PandasExprVisitor object at 0x7febc582c130>, node = <_ast.Constant object at 0x7febc582cd90>, kwargs = {'side': 'right'}, method = 'visit_Constant'
visitor = <bound method NodeVisitor.visit_Constant of <pandas.core.computation.expr.PandasExprVisitor object at 0x7febc582c130>>
    def visit(self, node, **kwargs):
        if isinstance(node, str):
            clean = self.preparser(node)
            try:
                node = ast.fix_missing_locations(ast.parse(clean))
            except SyntaxError as e:
                from keyword import iskeyword
                if any(iskeyword(x) for x in clean.split()):
                    e.msg = "Python keyword not valid identifier" " in numexpr query"
                raise e
        method = "visit_" + node.__class__.__name__
        visitor = getattr(self, method)
>       return visitor(node, **kwargs)
E       TypeError: visit_Constant() got an unexpected keyword argument 'side'
/usr/local/lib/python3.8/site-packages/pandas/core/computation/expr.py:441: TypeError

@blaklaybul found these issues which correspond to a pandas bug, which is fixed in pandas 0.25.2
pandas-dev/pandas#27261
pandas-dev/pandas#28101

After upgrading the pandas dependency to 0.25.2, the eland testsuite started failing in the following tests

=================================== FAILURES ===================================
__________________ TestDataFrameRepr.test_num_rows_repr_html ___________________
self = <eland.tests.dataframe.test_repr_pytest.TestDataFrameRepr object at 0x7f9da80ff3a0>
    def test_num_rows_repr_html(self):
        # check setup works
        assert pd.get_option('display.max_rows') == 60
        show_dimensions = pd.get_option('display.show_dimensions')
        # TODO - there is a bug in 'show_dimensions' as it gets added after the last </div>
        # For now test without this
        pd.set_option('display.show_dimensions', False)
        # Test eland.DataFrame.to_string vs pandas.DataFrame.to_string
        # In pandas calling 'to_string' without max_rows set, will dump ALL rows
        # Test n-1, n, n+1 for edge cases
>       self.num_rows_repr_html(pd.get_option('display.max_rows')-1)
eland/tests/dataframe/test_repr_pytest.py:166: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
self = <eland.tests.dataframe.test_repr_pytest.TestDataFrameRepr object at 0x7f9da80ff3a0>
rows = 59, max_rows = None
    def num_rows_repr_html(self, rows, max_rows=None):
        ed_flights = self.ed_flights()
        pd_flights = self.pd_flights()
        ed_head = ed_flights.head(rows)
        pd_head = pd_flights.head(rows)
        ed_head_str = ed_head._repr_html_()
        pd_head_str = pd_head._repr_html_()
        #print(ed_head_str)
        #print(pd_head_str)
>       assert pd_head_str == ed_head_str
E       AssertionError: assert '<div>\n<styl...able>\n</div>' == '<div>\n<styl...able>\n</div>'
E         Skipping 496 identical leading characters in diff, use -v to show
E         Skipping 146 identical trailing characters in diff, use -v to show
E           >
E         -       <th>0</th>
E         ?         ^     ^
E         +       <td>0</td>
E         ?         ^     ^...
E         
E         ...Full output truncated (640 lines hidden), use '-vv' to show
eland/tests/dataframe/test_repr_pytest.py:186: AssertionError
___________________________ TestSeriesRepr.test_repr ___________________________
self = <eland.tests.series.test_repr_pytest.TestSeriesRepr object at 0x7f9da80fe880>
    def test_repr(self):
        pd_s = self.pd_flights()['Carrier']
        ed_s = ed.Series(ELASTICSEARCH_HOST, FLIGHTS_INDEX_NAME, 'Carrier')
        pd_repr = repr(pd_s)
        ed_repr = repr(ed_s)
>       assert pd_repr == ed_repr
E       AssertionError: assert '0         Ki...dtype: object' == '0         Ki...dtype: object'
E         Skipping 291 identical leading characters in diff, use -v to show
E         -  Carrier, dtype: object
E         +  Carrier, Length: 13059, dtype: object
E         ?           +++++++++++++++
eland/tests/series/test_repr_pytest.py:17: AssertionError
======================== 2 failed, 74 passed in 22.68s =========================

[stevedodson]

Hopefully resolved by #91