Update the `filecmp.cmpfiles()` docs to match its actual signature.
file changes. The entire cache may be cleared using :func:`clear_cache`.
-.. function:: cmpfiles(dir1, dir2, common, shallow=True)
+.. function:: cmpfiles(a, b, common, shallow=True)
- Compare the files in the two directories *dir1* and *dir2* whose names are
+ Compare the files in the two directories *a* and *b* whose names are
given by *common*.
Returns three lists of file names: *match*, *mismatch*,