Fixes bug 1093792
Merge pull request #132 from anurag90x/Bug#1093792

Fixes bug 1093792
hash screencaptures with lower memory footprint
Merge pull request #133 from peterbe/hash-screencaptures-with-lower-memory-footprint

hash screencaptures with lower memory footprint
use pip cache in travis
Merge pull request #134 from peterbe/use-pip-cache-in-travis

use pip cache in travis