fixup! fixup! fixup! fixup! fixup! fixup! fixup! fixup! Fix Travis when SIX_VERSION isn't specificed

Author: gsnedders

requirements-install.sh

@@ -5,7 +5,8 @@ if [[ $USE_OPTIONAL != "true" && $USE_OPTIONAL != "false" ]]; then
   exit 1
 fi
 
-pip install pytest-expect\<2.0,\>=1.1
+pip install pytest-expect\<2.0,\>=1.1 six
+exit 2
 
 pip install -U setuptools wheel pip