Bump to Electron 11 beta

Electron 10 (and 9?) had glitchy behavior where some BrowserViews would
stop painting when the overlay view was removed and re-added.

webpack.config.js

@@ -72,7 +72,7 @@ const nodeConfig = {
 const browserConfig = {
   ...baseConfig({
     babel: {
-      presets: [['@babel/preset-env', { targets: { electron: '10' } }]],
+      presets: [['@babel/preset-env', { targets: { electron: '11' } }]],
     },
   }),
   devtool: 'cheap-source-map',