Fix argument name for 'it' in MSpec

Author: eregon

spec/mspec/lib/mspec/runner/object.rb

@@ -11,8 +11,8 @@ class Object
     MSpec.describe mod, msg, &block
   end
 
-  private def it(msg, &block)
-    MSpec.current.it msg, &block
+  private def it(desc, &block)
+    MSpec.current.it desc, &block
   end
 
   private def it_should_behave_like(desc)