```
Bundler could not find compatible versions for gem "activemodel":
In Gemfile:
activerecord was resolved to 5.2.0.alpha, which depends on activemodel (= 5.2.0.alpha)
rails (>= 3.0) was resolved to 4.2.9, which depends on activemodel (= 4.2.9)
```
Fix memory leak with :scope_name
Supplying :scope_name causes `ActiveModel::Serializer#initialize` to
define a method on the class, which retains a reference to the
serializer instance.
* Lock version of mime-types to < 3 for older JRubies
