Fix distribution deployment

Cache behavior of distributions require a list of trusted key groups,
but was being given a string value in our template,
exodus-lambda-deploy.yaml. This commit corrects the mistake.

configuration/exodus-lambda-deploy.yaml

@@ -88,7 +88,7 @@ Resources:
           TrustedKeyGroups:
             !If
               - EnableKeyGroup
-              - !Ref KeyGroup
+              - [!Ref KeyGroup]
               - !Ref AWS::NoValue
           ViewerProtocolPolicy: redirect-to-https
         Enabled: true