Add Snapchat + We Heart It to Forge Social Icon Pattern

[namimody]

http://forge.dosomething.org/#social-icon

Snapchat SVG available from: https://icomoon.io/

We Heart It SVG: https://dosomething.slack.com/files/nami/F1JHXN3RC/weheartit-01.svg

[DFurnes]

It'd also be nice to update to the new Instagram icon while we're in here.

[weerd]

Did you find that new one on icomoon? @DFurnes I can't locate it :\

[weerd]

Wait, just found it!