Modify requirements.txt - change Fabric to Fabric==1.11.1

[KenBuckley]

Hi the older version of fabric gives an error relating to Crypto , just upgrading the line in requrements.txt
to have the Fabric line read as follows:
Fabric==1.11.1
and running the following command :
pip install -r requirements.txt

will result in the Fab command working as expected.