Fix node fs mkdir

Author: SamyPesse

lib/fs/node.js

@@ -67,7 +67,7 @@ FS.prototype.write = function write(filePath, buf) {
 
     return this.mkdir(path.dirname(filePath))
     .then(function() {
-        return Promise.nfcall(this.fs.writeFile, that.path(filePath), buf);
+        return Promise.nfcall(that.fs.writeFile, that.path(filePath), buf);
     });
 };
 
@@ -86,6 +86,10 @@ FS.prototype.unlink = function unlink(filePath) {
  * @return {Promise}
  */
 FS.prototype.mkdir = function mkdir(filePath) {
+    if (this.fs.mkdirp) {
+        return Promise.nfcall(this.fs.mkdirp, this.path(filePath));
+    }
+
     return Promise.nfcall(mkdirp, this.path(filePath), {
         fs: this.fs
     });