Update proctortrack to fix a bug in json loading in python 3.

https://github.com/edx/edx-proctoring/pull/622

requirements/edx/base.txt

@@ -112,7 +112,7 @@ edx-oauth2-provider==1.3.1
 edx-opaque-keys[django]==2.0.1
 edx-organizations==2.1.1
 edx-proctoring-proctortrack==1.0.5
-edx-proctoring==2.1.5
+edx-proctoring==2.1.6
 edx-rbac==1.0.3           # via edx-enterprise
 edx-rest-api-client==1.9.2
 edx-search==1.2.2

requirements/edx/development.txt

@@ -135,7 +135,7 @@ edx-oauth2-provider==1.3.1
 edx-opaque-keys[django]==2.0.1
 edx-organizations==2.1.1
 edx-proctoring-proctortrack==1.0.5
-edx-proctoring==2.1.5
+edx-proctoring==2.1.6
 edx-rbac==1.0.3
 edx-rest-api-client==1.9.2
 edx-search==1.2.2

requirements/edx/testing.txt

@@ -132,7 +132,7 @@ edx-oauth2-provider==1.3.1
 edx-opaque-keys[django]==2.0.1
 edx-organizations==2.1.1
 edx-proctoring-proctortrack==1.0.5
-edx-proctoring==2.1.5
+edx-proctoring==2.1.6
 edx-rbac==1.0.3
 edx-rest-api-client==1.9.2
 edx-search==1.2.2