docs(api/index): grammar is important and so should you
docs(api/index): grammar is important and so should you

I changed the word "into" to "within".
Original description underneath ngAnimate reads: "Use ngAnimate to enable animation features into your application".
I changed the text to read: "Use ngAnimate to enable animation features within your application".
The change in wording makes the description read better and gives it a more professional feel.

Closes #10517

ggershoni/angular.js,ggershoni/angular.js,ggershoni/angular.js,ggershoni/angular.js