Please release persistent-template version 2.1.7 that supports ghc-8.0

[erikd]

Esqueleto still doesn't support persistent-2.5 but will build with ghc-8.0 if the upper bound on the base dependency is bumped (see prowdsponsor/esqueleto#135).

It would therefore be nice (and easy to do) to release a version of persistent-template that supports ghc-8.0.

If I checkout the persistent-template/2.1.6 tag as a branch I can then cherry pick commit 3adc3e6 which then builds and tests ok with both ghc-7.10 and ghc-8.0. I'd do a pull request, but I'm not sure how to do a pull request against something that is not a branch.

[snoyberg]

Awesome, done. Thanks for pushing these fixes all the way up the dependency tree :)