chore(functions/pubsub): use consistent param names (GoogleCloudPlatform#1997)

Author: Ace Nassri

functions/pubsub/index.js

@@ -37,9 +37,9 @@ const pubsub = new PubSub();
 exports.publish = async (req, res) => {
   if (!req.body.topic || !req.body.message) {
     res
-      .status(500)
+      .status(400)
       .send(
-        'Missing parameter(s); include "topic" and "subscription" properties in your request.'
+        'Missing parameter(s); include "topic" and "message" properties in your request.'
       );
     return;
   }

functions/pubsub/test/index.test.js

@@ -67,10 +67,10 @@ describe('functions/pubsub', () => {
         json: true,
       });
 
-      assert.strictEqual(response.statusCode, 500);
+      assert.strictEqual(response.statusCode, 400);
       assert.strictEqual(
         response.body,
-        'Missing parameter(s); include "topic" and "subscription" properties in your request.'
+        'Missing parameter(s); include "topic" and "message" properties in your request.'
       );
     });