fix hotspot gaze click using bind

[tommytee]

8966d4f broke gaze-to-click

.bind( this ) is used here (instead of an arrow function)

this pr is an es5 friendly version of #291

[googlebot]

We found a Contributor License Agreement for you (the sender of this pull request), but were unable to find agreements for the commit author(s). If you authored these, maybe you used a different email address in the git commits than was used to sign the CLA (login here to double check)? If these were authored by someone else, then they will need to sign a CLA as well, and confirm that they're okay with these being contributed to Google.
In order to pass this check, please resolve this problem and have the pull request author add another comment and the bot will run again. If the bot doesn't comment, it means it doesn't think anything has changed.

[jj-wd]

Has this been merged meanwhile? I'm unable to compile this branch currently due to some other issues but I downloaded the build files from gh-pages and gazing still doesn't seem to work?
Edit: Nevermind, I just added that line to the build file. Works perfectly.