updated pod command

I found your library while trying to find a way to use a GIF in iOS. 

I added the following to my Podfile but I was given an error.
 ```Ruby
 pod iOS_AnimatedGif
  ```

I searched around and found your CocoaPods page with AnimatedGif as the name. I used the following and it worked with no errors.
 ```Ruby
 pod 'AnimatedGif'
  ```

Thanks for the library!