Make autogrow return the selector wrapped for jQuery like most other plugins

I found this useful...something like `$('.my-textarea').autogrow().hide()` does not currently work because autogrow fails to follow the jQuery convention of returning a selector when possible.
Update autogrow.js
Update autogrow.min.js
Merge pull request #7 from Crisfole/patch-1

Make autogrow return the selector wrapped for jQuery like most other plu...