Update the 'global' check algorithm to latest umdjs guided

[fuweichin]

Overview:
gulp-umd templates is out of sync with umdjs templates.

The Problem:
As the 'global' check algorithm gulp-umd currently using in templates is deprecated, files generated gulp-umd have two serious problems:

• cannot be loaded with native ES module loader
  import '/node_modules/js-untar/build/dist/untar.js';
• not working properly in Firefox browser extension environment

The error looks like:

Cannot set property 'xxx' of undefined

because the outer this, or argument root in IIF, is undefined

see InvokIT/js-untar#30 and markedjs/marked#1292

Possible Solution:
Update the global check algorithm to umdjs's latest recommended way.

say, replace this with typeof self !== 'undefined' ? self : this, see returnExportsGlobal.js for example.

This is a serious problem, plz patch latest 3 versions (2.x, 1.x anf 0.2.x), also set deprecated tag on old versions at npm central registry.