Fix build - Support Seq[T] on LagomScala descriptor code generator

[ignasi35]

Build in Travis fails because a scripted test is not passing. That test failing is a consequence of a limited support for collection types in the LagomScala code generator (see also the invalid Integration Test).

Before proceeding with other issues, it is recommended to complete the LagomScala Descriptor generation to support Seq[T] in pathParams, Request and Response types.

See also lagom/lagom#643