Remove non-existing directories from Cask’s `.simplecov`.

Library/Homebrew/cask/.simplecov

 SimpleCov.start do
-  add_filter 'bin/'
-  add_filter 'Casks/'
-  add_filter 'developer/'
+  add_filter 'lib/vendor/'
   add_filter 'doc/'
   add_filter 'spec/'
   add_filter 'test/'