Changed placeholder support for Android 4 & 4.1

Android 4.0 and Android 4.1 Browser and WebView doesn't show up the placeholder for <input type=\"number\"> field, link: https://code.google.com/p/android/issues/detail?id=24626
Merge pull request #494 from Windstalker/patch-1

Changed placeholder support for Android 4 & 4.1