update javascript-obfuscator version to ^2.0.0.

Author: slig

README.md

@@ -1,6 +1,6 @@
 # grunt-contrib-obfuscator [![Build Status](https://travis-ci.com/javascript-obfuscator/grunt-contrib-obfuscator.svg?branch=master)](https://travis-ci.com/javascript-obfuscator/grunt-contrib-obfuscator)
 
-> Obfuscate JavaScript files using [javascript-obfuscator](https://github.com/javascript-obfuscator/javascript-obfuscator)@1.8.0.
+> Obfuscate JavaScript files using [javascript-obfuscator](https://github.com/javascript-obfuscator/javascript-obfuscator)@^2.0.0.
 
 You can try the javascript-obfuscator module and see all its options here: https://obfuscator.io/