set outline-color to -webkit-tap-highlight-color

There is an orange outline on focused elements in Android. This fix assumes that when tap-highlight-color is set, the outline color should be set to the same, clearing up the issue on Android. Fixes [#18357](https://bugs.dojotoolkit.org/ticket/18357).

![Android button focus highlight](https://cloud.githubusercontent.com/assets/293805/4945017/4492b2e0-6603-11e4-92e2-bf8fedcdac40.png)