remove mz from dependencies (gucong3000#19)

Author: gucong3000

lib/env.js

@@ -1,7 +1,7 @@
 'use strict';
 const path = require('path');
 const os = require('os');
-const exec = require('mz/child_process').execFile;
+const exec = require('util').promisify(require('child_process').execFile);
 const fs = require('fs-extra');
 const config = require('./config');
 

package.json

@@ -7,8 +7,7 @@
     "url": "https://github.com/gucong3000/mirror-config-china/issues"
   },
   "dependencies": {
-    "fs-extra": "^5.0.0",
-    "mz": "^2.6.0"
+    "fs-extra": "^5.0.0"
   },
   "description": "Mirrors in China about node.js",
   "devDependencies": {