Merge pull request getify#1009 from matthamil/patch-1

Typo in ch2: prinicple --> principle

Author: getify

es6 & beyond/ch2.md

@@ -1929,7 +1929,7 @@ var controller = {
 
 Lexical `this` in the arrow function callback in the previous snippet now points to the same value as in the enclosing `makeRequest(..)` function. In other words, `=>` is a syntactic stand-in for `var self = this`.
 
-In cases where `var self = this` (or, alternatively, a function `.bind(this)` call) would normally be helpful, `=>` arrow functions are a nicer alternative operating on the same prinicple. Sounds great, right?
+In cases where `var self = this` (or, alternatively, a function `.bind(this)` call) would normally be helpful, `=>` arrow functions are a nicer alternative operating on the same principle. Sounds great, right?
 
 Not quite so simple.