Update the Diesel buildpack

The new version caches the installed binary, and only re-installs when
the contents of `.diesel_version` changes.

Author: sgrif

.buildpacks

@@ -2,4 +2,4 @@ https://github.com/rcaught/heroku-buildpack-cmake#e4e2c9e
 https://github.com/mmirate/heroku-buildpack-rust#f1cf6643e
 https://github.com/tonycoco/heroku-buildpack-ember-cli
 https://github.com/ryandotsmith/nginx-buildpack.git#af813ba
-https://github.com/sgrif/heroku-buildpack-diesel#43267f2
+https://github.com/sgrif/heroku-buildpack-diesel#165d8b2

.diesel_version

@@ -0,0 +1 @@
+0.11.0