remove misleading class [ci skip]

guides/source/contributing_to_ruby_on_rails.md

@@ -205,7 +205,7 @@ Rails follows a simple set of coding style conventions:
 * Use Ruby >= 1.9 syntax for hashes. Prefer `{ a: :b }` over `{ :a => :b }`.
 * Prefer `&&`/`||` over `and`/`or`.
 * Prefer class << self over self.method for class methods.
-* Use `MyClass.my_method(my_arg)` not `my_method( my_arg )` or `my_method my_arg`.
+* Use `my_method(my_arg)` not `my_method( my_arg )` or `my_method my_arg`.
 * Use `a = b` and not `a=b`.
 * Use assert_not methods instead of refute.
 * Prefer `method { do_stuff }` instead of `method{do_stuff}` for single-line blocks.