Mock fix

lib/middleware.js

@@ -101,16 +101,17 @@ function mockResponses (route, targets) {
       }
 
       if (target) {
-        let mockedResponse = target.response
+        debug('target response: %j', target.response)
         if (t.isFunction(target.response)) {
           const pathMatches = ctx.url.match(pathRe).slice(1)
-          const ctor = target.response.bind(null, ...[ctx].concat(pathMatches))
-          mockedResponse = new ctor()
+          target.response.apply(null, [ctx].concat(pathMatches))
+        } else {
+          Object.assign(ctx.response, target.response)
         }
-        debug('target response: %j', mockedResponse)
-        Object.assign(ctx.response, mockedResponse)
+
       }
+    } else {
+      return next()
     }
-    return next()
   }
 }