remove descriptinos zip only supported by Python3

Author: minggli

pandas/core/frame.py

@@ -1655,9 +1655,8 @@ def to_csv(self, path_or_buf=None, sep=",", na_rep='', float_format=None,
             defaults to 'ascii' on Python 2 and 'utf-8' on Python 3.
         compression : string, optional
             a string representing the compression to use in the output file,
-            allowed values are 'gzip', 'bz2', 'zip', 'xz', 'zip' only
-            supported with Python>=3.0, only used when the first argument is a
-            filename.
+            allowed values are 'gzip', 'bz2', 'zip', 'xz', only used when the
+            first argument is a filename.
         line_terminator : string, default ``'\n'``
             The newline character or character sequence to use in the output
             file

pandas/core/generic.py

@@ -1816,8 +1816,7 @@ def to_json(self, path_or_buf=None, orient=None, date_format=None,
 
         compression : {None, 'gzip', 'bz2', 'zip', 'xz'}
             A string representing the compression to use in the output file,
-            'zip' only supported with Python>=3.0, only used when the first
-            argument is a filename.
+            only used when the first argument is a filename.
 
             .. versionadded:: 0.21.0
 
@@ -2089,8 +2088,7 @@ def to_pickle(self, path, compression='infer',
         compression : {'infer', 'gzip', 'bz2', 'zip', 'xz', None}, \
         default 'infer'
             A string representing the compression to use in the output file. By
-            default, infers from the file extension in specified path. 'zip'
-            only supported with Python>=3.0
+            default, infers from the file extension in specified path.
 
             .. versionadded:: 0.20.0
         protocol : int

pandas/io/pickle.py

@@ -20,8 +20,7 @@ def to_pickle(obj, path, compression='infer', protocol=pkl.HIGHEST_PROTOCOL):
         File path where the pickled object will be stored.
     compression : {'infer', 'gzip', 'bz2', 'zip', 'xz', None}, default 'infer'
         A string representing the compression to use in the output file. By
-        default, infers from the file extension in specified path. 'zip' only
-        supported with Python>=3.0
+        default, infers from the file extension in specified path.
 
         .. versionadded:: 0.20.0
     protocol : int