test-requirements.txt: Use custom pytest-reqs

pytest-reqs has problems with VCS requirements and versions.
The simplest solution at the moment is to skip these requirements.

Related to coala/meta#123

test-requirements.txt

@@ -13,7 +13,7 @@ pytest-instafail~=0.3.0
 pytest-mock~=1.1
 pytest-profiling~=1.3.0
 pytest-reorder~=0.1.0
-pytest-reqs~=0.0.6
+git+https://github.com/jayvdb/pytest-reqs@skip-vcs-reqs#egg=pytest-reqs
 pytest-timeout~=1.3.0
 pytest-travis-fold~=1.3.0
 pytest-xdist~=1.15