Watch gems.locked with Guard (#48)

Guard currently watches `Gemfile.lock`, but the site generated by
`utopia:site:create` uses `gems.locked` instead. Add `gems.locked` to
`Guardfile` so the dev env reloads as expected when the bundle changes.

Author: mjq

setup/site/Guardfile

@@ -3,6 +3,7 @@
 group :development do
 	guard :falcon, port: 9292 do
 		watch("Gemfile.lock")
+		watch("gems.locked")
 		watch("config.ru")
 		watch(%r{^config|lib|pages/.*})