grafana/toolkit: fix common webpack config (#18862)

packages/grafana-toolkit/src/config/webpack.plugin.config.ts

@@ -183,7 +183,7 @@ export const getWebpackConfig: WebpackConfigurationGetter = options => {
             {
               loader: 'babel-loader',
               options: {
-                presets: ['@babel/preset-env', { modules: false }],
+                presets: [['@babel/preset-env', { modules: false }]],
                 plugins: ['angularjs-annotate'],
               },
             },