Remove whitespace from json hash

Reasoning:

https://github.com/aanand/fig/commit/e5d8447f063498164f12567554a2eec16b4a3c88#commitcomment-11243708

Signed-off-by: Ben Firshman <[email protected]>

compose/utils.py

@@ -3,7 +3,7 @@ import hashlib
 
 
 def json_hash(obj):
-    dump = json.dumps(obj, sort_keys=True)
+    dump = json.dumps(obj, sort_keys=True, separators=(',', ':'))
     h = hashlib.sha256()
     h.update(dump)
     return h.hexdigest()