Upgrade to github-changelog-generator 0.0.7

Closes gh-298

Author: wilkinsona

ci/tasks/generate-changelog.yml

@@ -4,7 +4,7 @@ image_resource:
   type: registry-image
   source:
     repository: springio/github-changelog-generator
-    tag: '0.0.6'
+    tag: '0.0.7'
 inputs:
 - name: git-repo
 - name: artifactory-repo