Fix DateTime missing constant error on Ruby 1.9.3

Our tests were failing on Ruby 1.9.3. Adding this missing `require`
fixes them.

Change-Id: I0a9f0eb9fcc37202c072fdb83aa321d62e0360a6
Reviewed-on: http://gerrit.causes.com/42634
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>
Tested-by: Shane da Silva <shane.dasilva@brigade.com>
Remove debugger development dependency

We don't use this, and the `debugger` gem does not support Ruby 2.1.

Change-Id: Ib7d668c91ac9dd144fd224dd759fa0817441acf5
Reviewed-on: http://gerrit.causes.com/42635
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>
Tested-by: Shane da Silva <shane.dasilva@brigade.com>