Use the new develop WordPress repo for testing

Signed-off-by: Paul de Wouters <paul@hmn.md>
Change bootstrap

Signed-off-by: Paul de Wouters <paul@hmn.md>
fix plugin path for tests

Signed-off-by: Paul de Wouters <paul@hmn.md>
update paths

Signed-off-by: Paul de Wouters <paul@hmn.md>
Merge pull request #507 from humanmade/update-travis-tests

Use the new develop WordPress repo for testing