Fix the wrong agnoster.zsh-theme git symbol " " to "⭠"

Hello,

I am a Taiwanese who speak Chinese.
I recently setup the oh-my-zsh on my Ubuntu notebook and I found this error. (14.04)

![1](https://fbcdn-sphotos-d-a.akamaihd.net/hphotos-ak-xpf1/t1.0-9/10478200_687655454650813_6319359507623310327_n.jpg)

Fixed

![2](https://fbcdn-sphotos-c-a.akamaihd.net/hphotos-ak-xfa1/v/t1.0-9/10409606_687655511317474_1877507897809235685_n.jpg?oh=493a1d573a456c91602548bef3b4cf70&oe=545AB83D&__gda__=1412724235_699ef9b7ce2874721dfc1a98bc164ac5)