Update ruby-sinatra to 1.3.6.

= 1.3.6 (backport release) / 2013-03-15

Backported from 1.4.0:

* Take views option into account for template caching. (Konstantin Haase)

* Improve documentation (Konstantin Haase)

* No longer override `define_singleton_method`. (Konstantin Haase)

(obache)