Changed DIGIT.DIGIT to MAJOR.MINOR (#11281)

Closes #11122

Author: AR10X

docs/source/config_file.rst

@@ -323,7 +323,7 @@ Platform configuration
     :type: string
 
     Specifies the Python version used to parse and check the target
-    program.  The string should be in the format ``DIGIT.DIGIT`` --
+    program.  The string should be in the format ``MAJOR.MINOR`` --
     for example ``2.7``.  The default is the version of the Python
     interpreter used to run mypy.