"massage", "satellite", and other emoji don't work with this library.
The incompleteness, due to your reliance on the Phantom Open Emoji set, should be clearly spelled out at the top of the readme. This way, I may be the last person to waste an hour of his weekend digging through scripts and repos to find a really unexpected bug.
I like your gem otherwise, but it's called "emoji", implying that it's the Ruby library for handling those characters. The facts that it only handles some of them, and that you already knew about this issue but didn't tell us is bad form and frankly rude to your users.
Perhaps recommend this one instead?
You are he reason people burn out on open source. Don't be such an ass.
Oh, and also, you can use whatever image set you want, and it will work for those images. We have to use Phantom by default because distributing Apple Color Emoji is a copyright violation, which gemoji is currently violating