Webpack: don't cache build_config with @preval

webpack/rules/index.js

@@ -1,6 +1,7 @@
 const babel = require('./babel');
 const git = require('./babel-git');
 const gitRefresh = require('./git-refresh');
+const buildConfig = require('./babel-build-config');
 const css = require('./css');
 const file = require('./file');
 const nodeModules = require('./node_modules');
@@ -15,4 +16,5 @@ module.exports = [
   babel,
   git,
   gitRefresh,
+  buildConfig,
 ];