docs(guide/di): Use square bracket notation for $inject annotation

[ewinslow]

This recommendation is better as it ensures that the $inject property doesn't get minified when aggressively obfuscating code.

Re: CLA -- I work at Google.

[mary-poppins]

Thanks for the PR!

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Thanks again for your help!

[petebacondarwin]

@ewinslow - thanks for the PR. By the way, the commit message subject should not start with a capital letter.

[petebacondarwin]

At this line we are also using a property lookup rather than a square bracket dereference to actually get the property.
https://github.com/angular/angular.js/blob/master/src/auto/injector.js#L53

I guess you are not applying this aggressive obfuscation to the angular.js code?