fix(readme): make home image a link to github image

README.md

@@ -95,4 +95,4 @@ cache:
 
 Create a Github token that will be used to make commits and create releases.  Add the token to your travis environment variables as either `GH_TOKEN` or `GITHUB_TOKEN`.  Add the following permissions to your token:
 
-<img src="github-token-example.png" />
+<img src="https://raw.githubusercontent.com/conveyal/maven-semantic-release/master/github-token-example.png" />