Use inherits from npm instead of prototype.__proto__

I use browserify to use css on web browsers.

On internet explorer, `A.prototype.__proto__ = B.prototype;` leads to errors since IE can't access A's prototype.

If I use inherits module from npm, css works on IE9, IE10, chrome, firefox, and node.js without a problem.

To make css work on IE8, I have to replace ".import" with "['import']" because IE8 uses EcmaScript 3 engine in which "import" and "catch" are researved words and can't be used directly as object properties.
Thus, IE8 should not be considered.