dep: remove mkdirp dependency

* dep: mkdirp hasn't been updated in 4 years, and node's fs library
has had a recursive option for `fs` since v10.12 (oldest active LTS
version). Additionally `mkdirp` depends on a version of library `minimist` that has a minor vulnerability associated.

Refs:
* https://nodejs.org/api/fs.html#fs_fs_mkdir_path_options_callback
* https://npmjs.com/advisories/1179

lib/dir-writer.js

@@ -7,8 +7,8 @@
 module.exports = DirWriter
 
 var Writer = require('./writer.js')
+var nodeFs = require('fs')
 var inherits = require('inherits')
-var mkdir = require('mkdirp')
 var path = require('path')
 var collect = require('./collect.js')
 
@@ -31,7 +31,7 @@ function DirWriter (props) {
 
 DirWriter.prototype._create = function () {
   var self = this
-  mkdir(self._path, Writer.dirmode, function (er) {
+  nodeFs.mkdir(self._path, { recursive: true }, function (er) {
     if (er) return self.error(er)
     // ready to start getting entries!
     self.ready = true

lib/writer.js

@@ -1,9 +1,9 @@
 module.exports = Writer
 
+var nodeFs = require('fs')
 var fs = require('graceful-fs')
 var inherits = require('inherits')
 var rimraf = require('rimraf')
-var mkdir = require('mkdirp')
 var path = require('path')
 var umask = process.platform === 'win32' ? 0 : process.umask()
 var getType = require('./get-type.js')
@@ -166,7 +166,7 @@ function create (self) {
 
   // XXX Need to clobber non-dirs that are in the way,
   // unless { clobber: false } in the props.
-  mkdir(path.dirname(self._path), Writer.dirmode, function (er, made) {
+  nodeFs.mkdir(path.dirname(self._path), { recursive: true }, function (er, made) {
     // console.error("W created", path.dirname(self._path), er)
     if (er) return self.error(er)
 

package.json

@@ -14,7 +14,6 @@
   "dependencies": {
     "graceful-fs": "^4.1.2",
     "inherits": "~2.0.0",
-    "mkdirp": ">=0.5 0",
     "rimraf": "2"
   },
   "devDependencies": {