Update index.ngdoc

[erictheise]

Should either be "a different version" or "different versions"; this goes with the latter.

[googlebot]

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[erictheise]

Signed the CLA.

On Thu, Nov 27, 2014 at 9:17 AM, googlebot [email protected] wrote:

Thanks for your pull request.

It looks like this may be your first contribution to a Google open source
project, in which case you'll need to sign a Contributor License Agreement
(CLA) at https://cla.developers.google.com/.

If you've already signed a CLA, it's possible we don't have your GitHub
username or you're using a different email address. Check the information
on your CLA https://cla.developers.google.com/clas or see this help
article on setting the email on your git commits
https://help.github.com/articles/setting-your-email-in-git/.

Once you've done that, please reply here to let us know. If you signed the
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#10249 (comment).

[googlebot]

CLAs look good, thanks!