[flutter] Include example in pub.dev package.

spine-flutter/.pubignore

@@ -1,4 +1,3 @@
-example/
 !src/spine-cpp
 !ios/Classes/spine-cpp
 !macos/Classes/spine-cpp

spine-flutter/pubspec.yaml

@@ -46,7 +46,3 @@ flutter:
   assets:
     - lib/assets/libspine_flutter.js
     - lib/assets/libspine_flutter.wasm
-
-analyzer:
-  exclude:
-    - lib/init_web.dart