Enhance RSpec prepare command with JS build (#128)

Author: lukasbischof

lib/tasks/jsbundling/build.rake

@@ -13,6 +13,8 @@ end
 
 if Rake::Task.task_defined?("test:prepare")
   Rake::Task["test:prepare"].enhance(["javascript:build"])
+elsif Rake::Task.task_defined?("spec:prepare")
+  Rake::Task["spec:prepare"].enhance(["javascript:build"])
 elsif Rake::Task.task_defined?("db:test:prepare")
   Rake::Task["db:test:prepare"].enhance(["javascript:build"])
 end