fix eslint error

Author: xjlim

packages/react-scripts/config/webpackDevServer.config.js

@@ -75,7 +75,7 @@ module.exports = function(proxy, allowedHost) {
     // src/node_modules is not ignored to support absolute imports
     // https://github.com/facebookincubator/create-react-app/issues/1065
     watchOptions: {
-      ignored: new RegExp(`^(?!${paths.appSrc})*[\\\/]node_modules[\\\/]`, 'g'),
+      ignored: new RegExp(`^(?!${paths.appSrc})*[\\/]node_modules[\\/]`, 'g'),
     },
     // Enable HTTPS if the HTTPS environment variable is set to 'true'
     https: protocol === 'https',