add AssociationMatcher Scope

Author: radinreth

lib/liquid-rails/rspec/drop_matchers.rb

@@ -87,6 +87,11 @@ def class_name(class_name)
             self
           end
 
+          def scope(scope_name)
+            @options[:scope_name] = scope_name
+            self
+          end
+
           def description
             "have association #{name}"
           end