Add CI for py36,py37

[Julian]

[jayvdb]

I'm seeing a lot of errors on python 3.6 and 3.7, like

[  129s] _ test_linting_with_stdin_text[\n\nx = f(\n    _ for _ in range(2),\n)\n\n    ] _
[  129s] 
[  129s] monkeypatch = <_pytest.monkeypatch.MonkeyPatch object at 0x7fff8b4d7550>
[  129s] source = '\n\nx = f(\n    _ for _ in range(2),\n)\n\n    '
[  129s] 
[  129s]     @pytest.mark.parametrize('source', all_sources)
[  129s]     def test_linting_with_stdin_text(monkeypatch, source):
[  129s]         clean_source, error_locations = find_error_locations(source)
[  129s]         monkeypatch.setattr(pycodestyle, 'stdin_get_value',
[  129s]                             lambda: clean_source)
[  129s] >       assert_ebb_lint(clean_source, 'stdin', error_locations)
[  129s] 
[  129s] ebb_lint/test/test_flake8.py:1277: 
[  129s] _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
[  129s] ebb_lint/test/test_flake8.py:1232: in assert_ebb_lint
[  129s]     lint = EbbLint(ast.parse(source_text), source_path)
[  129s] _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
[  129s] 
[  129s] source = '\n\nx = f(\n    _ for _ in range(2),\n)\n\n', filename = '<unknown>'
[  129s] mode = 'exec'
[  129s] 
[  129s]     def parse(source, filename='<unknown>', mode='exec'):
[  129s]         """
[  129s]         Parse the source into an AST node.
[  129s]         Equivalent to compile(source, filename, mode, PyCF_ONLY_AST).
[  129s]         """
[  129s] >       return compile(source, filename, mode, PyCF_ONLY_AST)
[  129s] E         File "<unknown>", line 4
[  129s] E       SyntaxError: Generator expression must be parenthesized

and

[  156s] _ test_linting_with_stdin_text[\n\nspam = (\n    f(x)\n    for x in y\n    if p(x)\n)\n\n        ] _
[  156s] 
[  156s] monkeypatch = <_pytest.monkeypatch.MonkeyPatch object at 0xb6337fec>
[  156s] source = '\n\nspam = (\n    f(x)\n    for x in y\n    if p(x)\n)\n\n        '
[  156s] 
[  156s]     @pytest.mark.parametrize('source', all_sources)
[  156s]     def test_linting_with_stdin_text(monkeypatch, source):
[  156s]         clean_source, error_locations = find_error_locations(source)
[  156s]         monkeypatch.setattr(pycodestyle, 'stdin_get_value',
[  156s]                             lambda: clean_source)
[  156s] >       assert_ebb_lint(clean_source, 'stdin', error_locations)
[  156s] 
[  156s] ebb_lint/test/test_flake8.py:1277: 
[  156s] _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
[  156s] 
[  156s] source_text = '\n\nspam = (\n    f(x)\n    for x in y\n    if p(x)\n)\n\n'
[  156s] source_path = 'stdin', error_locations = []
[  156s] 
[  156s]     def assert_ebb_lint(source_text, source_path, error_locations):
[  156s]         lint = EbbLint(ast.parse(source_text), source_path)
[  156s]         actual = {
[  156s]             (line, col, message[:4]) for line, col, message, _ in lint.run()}
[  156s] >       assert actual == set(error_locations)
[  156s] E       AssertionError: assert {(6, 10, 'L201')} == set()
[  156s] E         Extra items in the left set:
[  156s] E         (6, 10, 'L201')
[  156s] E         Full diff:
[  156s] E         - {(6, 10, 'L201')}
[  156s] E         + set()
[  156s] 
[  156s] ebb_lint/test/test_flake8.py:1235: AssertionError

openSUSE build happening at https://build.opensuse.org/package/show/home:jayvdb:flake8/python-ebb-lint