Fix style errors and unpin pylint/asteroid versions

functional/pipeline.py

@@ -1463,6 +1463,7 @@ def dict(self, default=None):
         """
         return self.to_dict(default=default)
 
+    # pylint: disable=too-many-locals
     def to_file(self, path, delimiter=None, mode='wt', buffering=-1, encoding=None, errors=None,
                 newline=None, compresslevel=9, format=None, check=-1, preset=None, filters=None,
                 compression=None):

functional/streams.py

@@ -203,6 +203,7 @@ def json(self, json_file):
         else:
             return self(six.viewitems(json_input))
 
+    # pylint: disable=keyword-arg-before-vararg
     def sqlite3(self, conn, sql, parameters=None, *args, **kwargs):
         """
         Reads input by querying from a sqlite database.

functional/util.py

@@ -127,6 +127,7 @@ def unpack(packed):
     result = func(*args)
     if isinstance(result, collections.Iterable):
         return list(result)
+    return None
 
 
 def pack(func, args):

travis.sh

@@ -2,12 +2,7 @@
 
 set -e
 
-if [[ $PY_36 -eq 1 ]]; then
-    pip install git+https://github.com/PyCQA/pylint.git@7daed7b8982480c868b0f642a5251f00ffb253c6
-    pip install git+https://github.com/PyCQA/astroid.git@d0b5acdfebcdda5c949584c32a8cbc0f31d5cf25
-else
-    pip install pylint
-fi
+pip install pylint
 
 if ! [[ $PYPY -eq 1 ]]; then
     pip install pandas