docs: fix simple typo, assigining -> assigning

There is a small typo in patterns/creational/borg.py.

Should read `assigning` rather than `assigining`.

Author: timgates42

patterns/creational/borg.py

@@ -13,7 +13,7 @@
 its own dictionary, but the Borg pattern modifies this so that all
 instances have the same dictionary.
 In this example, the __shared_state attribute will be the dictionary
-shared between all instances, and this is ensured by assigining
+shared between all instances, and this is ensured by assigning
 __shared_state to the __dict__ variable when initializing a new
 instance (i.e., in the __init__ method). Other attributes are usually
 added to the instance's attribute dictionary, but, since the attribute