annotate --routes modifies only routes.rb

This change is a proposed solution to ctran#357 and an alternative to the already proposed solution ctran#361.
In ctran#361 it is needed to call `annotate --routes --ignore-models` to achieve the same as in this change with only `annotate --routes`.

Author: Hitabis

lib/annotate.rb

@@ -114,7 +114,7 @@ def self.include_routes?
   end
 
   def self.include_models?
-    true
+    ENV['routes'] !~ TRUE_RE
   end
 
   def self.loaded_tasks=(val)