[tox] Don't add requirement.txt to deps.

tox.ini

@@ -2,7 +2,7 @@
 envlist = py27, py35
 
 [testenv]
-commands = 
+commands =
     {envbindir}/py.test --cov=dosage --cov=dosagelib --tb=short -n4 \
         --cov-report=xml:{toxworkdir}/cov-{envname}.xml --cov-report=term \
         --junitxml={toxworkdir}/junit-{envname}.xml {posargs}
@@ -10,7 +10,6 @@ commands =
 passenv = TRAVIS
 # Also install optional dependencies for tests.
 deps =
-    -rrequirements.txt
     pytest-xdist
     pytest-cov
     pytest-travis-fold