feat: Update package.json to 1.2.1

Author: github-actions[bot]

src/GrpcWebSocketBridge.Client.Unity/Assets/Plugins/GrpcWebSocketBridge/package.json

@@ -2,7 +2,7 @@
     "name": "com.cysharp.grpcwebsocketbridge",
     "displayName": "GrpcWebSocketBridge",
     "author": { "name": "Cysharp, Inc.", "url": "https://cysharp.co.jp/en/" },
-    "version": "1.2.0",
+    "version": "1.2.1",
     "unity": "2019.4",
     "description": "",
     "keywords": ["WebSocket", "gRPC"],