Fix vcrpy's version to avoid breaking python 3.4 build

requirements.txt

@@ -1,7 +1,7 @@
 futures;python_version<="2.7"
 python-dateutil
 requests>=2.9.2
-vcrpy
+vcrpy<2.0.0 #2.0 breaks python 3.4
 azure-common
 cryptography>=1.3.0;python_version!="3.3"
 cryptography<=1.9.0;python_version=="3.3"