Merge pull request #23 from grapl-security/cm/plugin-tester-v3.0.0

Update `buildkite/plugin-tester to v3.0.0

Author: christophermaier

docker-compose.yml

@@ -8,7 +8,7 @@ x-common-variables:
 
 services:
   plugin-tester:
-    image: buildkite/plugin-tester:v2.0.0
+    image: buildkite/plugin-tester:v3.0.0
     volumes:
       - *read-only-plugin