Well I just changed my config.xml following property to false and it combined the build apk.
from
<preference name="xwalkMultipleApk" value="true"/>
to
<preference name="xwalkMultipleApk" value="false"/>
My systems ionic info returns
Your system information:
Cordova CLI: 6.1.1
Gulp version: CLI version 3.9.1
Gulp local: Local version 3.9.1
Ionic CLI Version: 1.7.16
Ionic App Lib Version: 0.7.3
OS:
Node Version: v4.4.4