fix(file): add toInternalURL (#1561)

* Put back toInternalURL

What was the reason to remove `toInternalURL` from `Entry`?
Fixes #1560

* Remove trailing whitespace

src/@ionic-native/plugins/file/index.ts

@@ -159,6 +159,12 @@ export interface Entry {
    */
   toURL(): string;
 
+  /**
+   * Return a URL that can be passed across the bridge to identify this entry.
+   * @return string URL that can be passed across the bridge to identify this entry
+   */
+  toInternalURL(): string;
+
   /**
    * Deletes a file or directory. It is an error to attempt to delete a directory that is not empty. It is an error to attempt to delete the root directory of a filesystem.
    * @param successCallback A callback that is called on success.