chore(plugin.xml): ✨ declare the opentok file in the js-module

It makes the opentok file show up in the cordova_plugin.js file.
It enables the `cordova-plugin-injectview` plugin to properly detect and inject the opentok files.

plugin.xml

@@ -9,6 +9,10 @@
     <license>Apache 2.0</license>
     <keywords>opentok,tokbox</keywords>
 
+    <js-module src="www/opentok.js" name="opentok">
+      <runs />
+    </js-module>
+
     <platform name="android">
       <framework src="build-extras.gradle" custom="true" type="gradleReference" />
       <framework src="com.android.support:appcompat-v7:23.1.0" />