Fixed some dependency versions due to issues with current releases.

requirements.txt

@@ -11,13 +11,14 @@ Pint==0.7.2
 matid
 
 # infrastructue related
+elasticsearch==6.4.0
+elasticsearch-dsl==6.4.0
 msgpack<0.6.0
 pyyaml
 future
 enum34
 requests
 celery[redis]
-elasticsearch-dsl>=6.0.0,<7.0.0
 mongoengine==0.18.2
 Werkzeug==0.16.1
 flask
@@ -38,7 +39,7 @@ zipstream-new==1.1.5
 bagit
 bcrypt
 filelock
-ujson
+ujson==1.35
 bravado
 pyjwt[crypto]
 jsonschema[format]