Update drf-nested-routers from 0.90.2 to 0.91

requirements/prod_common.txt

@@ -185,9 +185,9 @@ djangorestframework-jwt==1.11.0 \
 dockerflow==2018.4.0 \
     --hash=sha256:388d02c557968e6957140f7b82f669eac70adf5f570bc7705aa749d220a2e535 \
     --hash=sha256:2ea52a904abfda3430ff4f1effc164863b30d2b69f7ecbf92dd672860b0ec423
-drf-nested-routers==0.90.2 \
-    --hash=sha256:a4d97de1be554f5db3fd11c881f578d10a3e1324b6e99be1749a11c7248d3360 \
-    --hash=sha256:52cbc4900e3ccd652bfb73017ff466d7b3e4d99838c912c250d75763b32669af
+drf-nested-routers==0.91 \
+    --hash=sha256:60c1e1f5cc801e757d26a8138e61c44419ef800c213c3640c5b6138e77d46762 \
+    --hash=sha256:46e5c3abc15c782cafafd7d75028e8f9121bbc6228e3599bbb48a3daa4585034
 easy-thumbnails==2.5 \
     --hash=sha256:e244d1f26027fc32c6ca60ffb0169a39099446f614b0433e907a2588ae7d9b95
 # elasticsearch is required by elasticsearch-dsl