Increase min-similarity-lines

Increase the value to suppress the warning for common context
manager code.

I would have liked to disable the warning R0801 locally, but it
doesn't seem to be possible. See also
pylint-dev/pylint#214 .

pylintrc

@@ -148,7 +148,7 @@ no-docstring-rgx=__.*__
 [SIMILARITIES]
 
 # Minimum lines number of a similarity.
-min-similarity-lines=4
+min-similarity-lines=5
 
 # Ignore comments when computing similarities.
 ignore-comments=yes