Support servant-server-0.19.1

[nbacquey]

Since version 0.19.1, servant-server requires the type a in combinator Capture foo a to be Typeable. This commit adds the constraint in HasMock for Capture' and CaptureAll

[arjunkathuria]

hi @nbacquey,

Did you try running the test suite for this?

I patched the library for the same during upgrading a project and it builds, but when you run the tests for this, they fail.

[nbacquey]

This later version should work, the test suite passes. The Fragment a keyword was also recently introduced in Servant, and hadn't a HasMock instance yet, which I've added.

[domenkozar]

We're using this, any chance to merge?