Revert "Install Test::Nginx from git repo (for on_abort testing #67)"

This reverts commit 16cf72135d057f3800bfb61c31edbdf67a367063.

We should resolve this by getting the cpan package updated rather than screwing about with the git version :)

Signed-off-by: Ben Agricola <bagricola@squiz.co.uk>

Conflicts:
	.travis.yml