Omit Chrome stable in travis for now

The default Chrome in travis is Chrome *37*.  Disabling - will a send
a separate CL to fix properly.

TBR=jmesserly@google.com

Review URL: https://codereview.chromium.org/1331963002 .

Author: vsmenon

karma.conf.js

@@ -102,7 +102,7 @@ module.exports = function(config) {
   };
 
   if (process.env.TRAVIS) {
-    configuration.browsers = ['chrome_travis', 'chrome_canary_travis'];
+    configuration.browsers = ['chrome_canary_travis'];
     configuration.autoWatch = false;
     configuration.logLevel = config.LOG_DEBUG;
     configuration.client.captureConsole = true;