react-hot-loader: Disable safetyNet to work with ESM

After upgrading webpack and plugins/loaders, there was an error from
react-hot-loader:

    ReferenceError: module is not defined

A known workaround is to enable safetyNet [1] so the code referencing
`module` is not executed.

I'm not sure why this was not shown before the webpack upgrades, but
don't feel like digging deeper to find out.

[1]: gaearon/react-hot-loader#1102 (comment)

babel.config.js

@@ -27,7 +27,7 @@ module.exports = function babelConfig(api) {
     "lodash"
   ];
   if (api.env("development")) {
-    plugins.push("react-hot-loader/babel");
+    plugins.push(["react-hot-loader/babel", { safetyNet: false }]);
   }
   if (process.env.BABEL_INCLUDE_TIMING_FUNCTIONS === "false") {
     plugins.push(["strip-function-call", {strip: ["timerStart", "timerEnd"]}]);