fix setting of title.text

Author: emilykl

test/jasmine/tests/transition_test.js

@@ -455,7 +455,7 @@ describe('Plotly.react transitions:', function() {
             ]);
         })
         .then(function() {
-            layout.title.text = 'FIGURE';
+            layout.title = { text: 'FIGURE' };
             return Plotly.react(gd, data, layout);
         })
         .then(function() {