Update platform interface version

Author: Eunchul Jeon

packages/webview_flutter/webview_flutter_android/example/pubspec.yaml

@@ -17,8 +17,7 @@ dependencies:
     # The example app is bundled with the plugin so we use a path dependency on
     # the parent directory to use the current plugin's version.
     path: ../
-  webview_flutter_platform_interface:
-    path: ../../webview_flutter_platform_interface
+  webview_flutter_platform_interface: ^2.7.0
 
 dev_dependencies:
   espresso: ^0.2.0

packages/webview_flutter/webview_flutter_android/pubspec.yaml

@@ -20,8 +20,7 @@ flutter:
 dependencies:
   flutter:
     sdk: flutter
-  webview_flutter_platform_interface:
-    path: ../webview_flutter_platform_interface
+  webview_flutter_platform_interface: ^2.7.0
 
 dev_dependencies:
   build_runner: ^2.1.4

packages/webview_flutter/webview_flutter_wkwebview/example/pubspec.yaml

@@ -10,8 +10,7 @@ dependencies:
   flutter:
     sdk: flutter
   path_provider: ^2.0.6
-  webview_flutter_platform_interface:
-    path: ../../webview_flutter_platform_interface
+  webview_flutter_platform_interface: ^2.7.0
   webview_flutter_wkwebview:
     # When depending on this package from a real application you should use:
     #   webview_flutter: ^x.y.z

packages/webview_flutter/webview_flutter_wkwebview/pubspec.yaml

@@ -20,8 +20,7 @@ dependencies:
   flutter:
     sdk: flutter
   path: ^1.8.0
-  webview_flutter_platform_interface:
-    path: ../webview_flutter_platform_interface
+  webview_flutter_platform_interface: ^2.7.0
 
 dev_dependencies:
   build_runner: ^2.1.5