chore: Require android 9 (apache#439)

* chore: bump version to 7.0.0-dev

* chore: bump android engine requirement

Author: breautek

package.json

@@ -36,6 +36,9 @@
       "5.0.0": {
         "cordova-android": ">=6.3.0"
       },
+      "7.0.0": {
+        "cordova-android": ">=9.0.0"
+      },
       "8.0.0": {
         "cordova": ">100"
       }

plugin.xml

@@ -30,7 +30,7 @@ xmlns:android="http://schemas.android.com/apk/res/android"
     <issue>https://github.com/apache/cordova-plugin-file/issues</issue>
 
     <engines>
-        <engine name="cordova-android" version=">=6.3.0" />
+        <engine name="cordova-android" version=">=9.0.0" />
     </engines>
 
     <js-module src="www/DirectoryEntry.js" name="DirectoryEntry">