Ruby: ignore RuboCop remote inherited config files (#3197)

Ruby.gitignore

@@ -51,3 +51,6 @@ build-iPhoneSimulator/
 
 # unless supporting rvm < 1.11.0 or doing something fancy, ignore this:
 .rvmrc
+
+# Used by RuboCop. Remote config files pulled in from inherit_from directive.
+# .rubocop-https?--*