capitalization correction for Counter title (#206)

* Update collections.rst

* parallel sorting bug fix

Python 3 zip object no longer supports .sort()
AttributeError: 'zip' object has no attribute 'sort'

Changed to sorted to be forward compatible

Author: LeChn

collections.rst

@@ -9,7 +9,7 @@ The ones which we will talk about are:
 
 -  ``defaultdict``
 -  ``OrderedDict``
--  ``counter``
+-  ``Counter``
 -  ``deque``
 -  ``namedtuple``
 -  ``enum.Enum`` (outside of the module; Python 3.4+)
@@ -119,7 +119,7 @@ the end of the dictionary.
     #   Blue 160
     # Insertion order is preserved
 
-``counter``
+``Counter``
 ^^^^^^^^^^^^^^^
 
 Counter allows us to count the occurrences of a particular item. For

lambdas.rst

@@ -39,5 +39,5 @@ they are used in the wild:
 .. code:: python
 
     data = zip(list1, list2)
-    data.sort()
+    data = sorted(data)
     list1, list2 = map(lambda t: list(t), zip(*data))