Remove context reference from CircleCI (#1534)

Author: rpkyle

.circleci/config.yml

@@ -409,28 +409,20 @@ workflows:
   version: 2
   python3.7:
     jobs:
-      - lint-unit-37:
-          context: dash-docker-hub
-      - build-core-37:
-          context: dash-docker-hub
-      - build-windows-37:
-          context: dash-docker-hub
-      - build-misc-37:
-          context: dash-docker-hub
-      - build-dashr:
-          context: dash-docker-hub
+      - lint-unit-37
+      - build-core-37
+      - build-windows-37
+      - build-misc-37
+      - build-dashr
       - test-37:
-          context: dash-docker-hub
           requires:
             - build-core-37
             - build-misc-37
       - percy-finalize:
-          context: dash-docker-hub
           requires:
             - build-dashr
             - test-37
       - artifacts:
-          context: dash-docker-hub
           requires:
             - percy-finalize
           filters:
@@ -443,27 +435,19 @@ workflows:
 
   python3.6:
     jobs:
-      - lint-unit-36:
-          context: dash-docker-hub
-      - build-core-36:
-          context: dash-docker-hub
-      - build-misc-36:
-          context: dash-docker-hub
+      - lint-unit-36
+      - build-core-36
+      - build-misc-36
       - test-36:
-          context: dash-docker-hub
           requires:
             - build-core-36
             - build-misc-36
   python2.7:
     jobs:
-      - lint-unit-27:
-          context: dash-docker-hub
-      - build-core-27:
-          context: dash-docker-hub
-      - build-misc-27:
-          context: dash-docker-hub
+      - lint-unit-27
+      - build-core-27
+      - build-misc-27
       - test-27:
-          context: dash-docker-hub
           requires:
             - build-core-27
             - build-misc-27