update dynamo exception to struct & record to Record for elixir 0.13.3
Merge pull request #236 from xbinxu/master

update dynamo exceptions/records/Mix.Project for elixir 0.13.3
Update mime dependency
Update mix.exs
use stable Elixir branch on travis
Merge pull request #238 from herenowcoder/upstream

use stable Elixir branch on travis
Remove dependency on hygiene: false
Make it clearer that Dynamo is in maintenence mode