add type to webview style tag

lib/renderer/web-view/web-view.js

@@ -31,7 +31,7 @@ var WebViewImpl = (function () {
     this.on = {}
     this.browserPluginNode = this.createBrowserPluginNode()
     shadowRoot = this.webviewNode.createShadowRoot()
-    shadowRoot.innerHTML = '<style>:host { display: flex; }</style>'
+    shadowRoot.innerHTML = '<style type="text/css">:host { display: flex; }</style>'
     this.setupWebViewAttributes()
     this.setupFocusPropagation()
     this.viewInstanceId = getNextId()