chore: fix eslint in cache-dir/loader (#9002)

# Overview
I've tried fixing #6300, I  encountered 2 ESLInt error.
In original Google Translate Issue, I'm considering how approach to fix🤔

<img width="1241" alt="screen shot 2018-10-11 at 2 15 14" src="https://user-images.githubusercontent.com/5501268/46754799-5125ee80-ccfe-11e8-81dd-646a3bd74dee.png">

packages/gatsby/cache-dir/loader.js

@@ -166,13 +166,6 @@ const onPostPrefetchPathname = pathname => {
 // let pathArray = []
 // let pathCount = {}
 
-let resourcesCount = Object.create(null)
-const sortResourcesByCount = (a, b) => {
-  if (resourcesCount[a] > resourcesCount[b]) return 1
-  else if (resourcesCount[a] < resourcesCount[b]) return -1
-  else return 0
-}
-
 let findPage
 let pathScriptsCache = {}
 let prefetchTriggered = {}
@@ -290,7 +283,8 @@ const queue = {
           path,
           `Previously detected load failure for "${path}"`
         )
-        return reject()
+        reject()
+        return
       }
       const page = findPage(path)
 
@@ -303,20 +297,23 @@ const queue = {
       ) {
         // If page wasn't found check and we didn't fetch resources map for
         // all pages, wait for fetch to complete and try to get resources again
-        return fetchPageResourceMap().then(() =>
+        fetchPageResourceMap().then(() =>
           resolve(queue.getResourcesForPathname(path))
         )
+        return
       }
 
       if (!page) {
         console.log(`A page wasn't found for "${path}"`)
 
         // Preload the custom 404 page
         if (path !== `/404.html`) {
-          return resolve(queue.getResourcesForPathname(`/404.html`))
+          resolve(queue.getResourcesForPathname(`/404.html`))
+          return
         }
 
-        return resolve()
+        resolve()
+        return
       }
 
       // Use the path from the page so the pathScriptsCache uses
@@ -329,7 +326,8 @@ const queue = {
           page,
           pageResources: pathScriptsCache[path],
         })
-        return resolve(pathScriptsCache[path])
+        resolve(pathScriptsCache[path])
+        return
       }
 
       // Nope, we need to load resource(s)