Improve code readability

Refine method argument check for clarity: Both
`(method.arity + args.size == 0)` and `(method.arity + args.size) == 0`
are equivalent due to operator precedence, but the latter is preferred
for improved readability.

Close #56

lib/hawk/model/proxy.rb

@@ -98,7 +98,7 @@ def method_missing(meth, *args, &block)
 
           # If the method accepts a variable number of parameters, and
           # the last provided one is an hash, merge the scoped params.
-          elsif method.arity < 0 && (method.arity + args.size == 0) && args.last.is_a?(Hash)
+          elsif method.arity < 0 && (method.arity + args.size) == 0 && args.last.is_a?(Hash)
             args[-1] = params.deep_merge(args[-1])
 
           end