Update error message to reflect new usage

Author: thomseddon

lib/grant.js

@@ -73,8 +73,7 @@ function extractCredentials (done) {
   // Grant type
   this.grantType = this.req.body && this.req.body.grant_type;
   if (!this.grantType) {
-    return done(error('invalid_request',
-      'Invalid or missing grant_type parameter'));
+    return done(error('invalid_request', 'Missing grant_type parameter'));
   } else if (!this.grantType.match(this.config.regex.grantType)) {
     return done(error('unsupported_grant_type', 'Unsupported grant type'));
   }

test/grant.js

@@ -72,7 +72,7 @@ describe('Grant', function() {
       request(app)
         .post('/oauth/token')
         .set('Content-Type', 'application/x-www-form-urlencoded')
-        .expect(400, /invalid or missing grant_type parameter/i, done);
+        .expect(400, /missing grant_type parameter/i, done);
     });
 
     it('should ensure grant_type is allowed', function (done) {