use API for coloring

src/com/owncloud/android/utils/DisplayUtils.java

@@ -290,8 +290,6 @@ public class DisplayUtils {
      */
     public static void colorSnackbar(Context context, Snackbar snackbar) {
         // Changing action button text color
-        View sbView = snackbar.getView();
-        TextView textView = (TextView) sbView.findViewById(android.support.design.R.id.snackbar_action);
-        textView.setTextColor(ContextCompat.getColor(context, R.color.white));
+        snackbar.setActionTextColor(ContextCompat.getColor(context, R.color.white));
     }
 }