Upgraded development requirements to speed up code coverage recording

Removed requests from requirements.txt file, because it's already a req
of pillar-python-sdk.

requirements-dev.txt

@@ -3,13 +3,13 @@
 -e .
 
 # Development requirements
-pytest==3.0.1
+pytest==3.0.6
 responses==0.5.1
-pytest-cov==2.3.1
+pytest-cov==2.4.0
 mock==2.0.0
 
 # Secondary development requirements
 cookies==2.2.1
-coverage==4.0.3
-pbr==1.9.1
+coverage==4.3.4
+pbr==2.0.0
 py==1.4.31