Fix "EXDEV: cross-device link not permitted" error (#1174)

* Fix "EXDEV: cross-device link not permitted" error

* Fix lint errors

Not sure why standard passes in my dev environment, but hopefully this fixes the CI errors.

* Fix logic mistake

Wow, my bad :/

package.json

@@ -70,6 +70,7 @@
     "loader-utils": "0.2.16",
     "minimist": "1.2.0",
     "mkdirp-then": "1.2.0",
+    "mv": "^2.1.1",
     "mz": "2.6.0",
     "path-match": "1.2.4",
     "pkg-up": "1.0.0",

server/build/replace.js

-import { rename } from 'mz/fs'
+import mv from 'mv'
 import { join } from 'path'
 
 export default async function replaceCurrentBuild (dir, buildDir) {
@@ -7,10 +7,15 @@ export default async function replaceCurrentBuild (dir, buildDir) {
   const oldDir = join(buildDir, '.next.old')
 
   try {
-    await rename(_dir, oldDir)
+    await move(_dir, oldDir)
   } catch (err) {
     if (err.code !== 'ENOENT') throw err
   }
-  await rename(_buildDir, _dir)
+  await move(_buildDir, _dir)
   return oldDir
 }
+
+function move (from, to) {
+  return new Promise((resolve, reject) =>
+    mv(from, to, err => err ? reject(err) : resolve()))
+}