Merge pull request #406 from manu-chroma/master

requirements.txt: use same version of rdflib as in setup.py and schema_salad

Author: mr-c

requirements.txt

@@ -1,6 +1,6 @@
 requests>=1.0
 ruamel.yaml==0.13.7
-rdflib==4.2.1
+rdflib==4.2.2
 rdflib-jsonld==0.4.0
 shellescape==3.4.1
 schema-salad>=2.4.20170308171942,<3