Log Message:
Update heel 3.1.3.

## Version 3.1.3 - 2013-11-26
* URL encode the links to files \ 
[#14](https://github.com/copiousfreetime/heel/issues/14)
* Fix pid file cleanup on ruby 2.0 \ 
[#15](https://github.com/copiousfreetime/heel/issues/15)

## Version 3.1.2 - 2013-10-16
* Fix usage of Mime::Types \ 
[#12](https://github.com/copiousfreetime/heel/issues/12) \ 
[#13](https://github.com/copiousfreetime/heel/issues/13)

## Version 3.1.1 - 2013-09-29
* Fix request logging [#10](https://github.com/copiousfreetime/heel/issues/10)