Make cordova-android 7.x mandatory

With Tabris.js 3.0 the project migrates to cordova-android 7.x.

Author: mpost

plugin.xml

@@ -13,7 +13,7 @@
 
   <!-- cordova -->
   <engines>
-    <engine name="cordova" version=">=3.8.0" />
+    <engine name="cordova-android" version=">=7.0.0" />
   </engines>
 
   <js-module src="www/Messaging.js" name="messaging">