Update ruby-sinatra to 1.4.5.

= 1.4.5 / 2014-04-08

* Improve tests and documentation. (Seiichi Yonezawa, Mike Gehard, Andrew
  Deitrick, Matthew Nicholas Bradley, GoGo tanaka, Carlos Lazo, Shim Tw,
  kyoendo, Roman Kuznietsov, Stanislav Chistenko, Ryunosuke SATO, Ben Lewis,
  wuleicanada, Patricio Mac Adden, Thais Camilo)

* Fix Ruby warnings. (Vipul A M, Piotr Szotkowski)

* Fix template cache memory leak. (Scott Holden)

* Work around UTF-8 bug in JRuby. (namusyaka)

* Don't set charset for JSON mime-type (Sebastian Borrazas)

* Fix bug in request.accept? that might trigger a NoMethodError. (sbonami)

(taca)