Don't use deprecated process.umask() (#791)

* Don't use deprecated process.umask()

Refs sindresorhus/make-dir#27

* Remove unneeded umask tests

No need to test Node.js core's behavior (which is all these tests do)

Author: RyanZim

lib/mkdirs/__tests__/umask.test.js

@@ -25,8 +25,7 @@ const checkPath = pth => {
 }
 
 const processOptions = options => {
-  // Must be defined here so we get fresh process.umask()
-  const defaults = { mode: 0o777 & (~process.umask()) }
+  const defaults = { mode: 0o777 }
   if (typeof options === 'number') options = { mode: options }
   return { ...defaults, ...options }
 }