Cleanup build-javascript (#22033)

* Cleanup build-javascript

* Update build-javascript.ts

* Cleanup even more

packages/gatsby/src/commands/build-javascript.ts

@@ -1,7 +1,9 @@
+import { Span } from "opentracing"
 import webpack from "webpack"
+
 import webpackConfig from "../utils/webpack.config"
+
 import { IProgram } from "./types"
-import { Span } from "opentracing"
 
 import { reportWebpackWarnings } from "../utils/webpack-error-utils"
 
@@ -22,18 +24,16 @@ export const buildProductionBundle = async (
   return new Promise((resolve, reject) => {
     webpack(compilerConfig).run((err, stats) => {
       if (err) {
-        reject(err)
-        return
+        return reject(err)
       }
 
       reportWebpackWarnings(stats)
 
       if (stats.hasErrors()) {
-        reject(stats.compilation.errors)
-        return
+        return reject(stats.compilation.errors)
       }
 
-      resolve(stats)
+      return resolve(stats)
     })
   })
 }