fix self reference in completion block.

  * ISRefreshControl.m
    * change wself type to __block.
    * fix to use wself in completion block.

  * .gitignore
    * add xcuserdata, .DS_Store to .gitignore.

  * Podfile
    * remove ISMethodSwizzling from Podfile because already included.
      * ishkawa/ISRefreshControl@689048391db1ff3c9f9d046f3c15429ff5e7a655