Fix template and variables

.gitlab/.readme_variables

 export GITHUB_REPONAME='docker-SUI'
 export GITHUB_USERNAME='Griefed'
-export GITHUB_REPONAME_header='docker-SUI_header.png'
-export GITHUB_REPONAME_screenshot='docker-SUI_screenshot.png'
+export GITHUB_REPONAME_HEADER='docker-SUI_header.png'
+export GITHUB_REPONAME_SCREENSHOT='docker-SUI_screenshot.png'
 export DOCKERHUB_REPONAME='sui'
 export DOCKERHUB_TAG='latest'
 export DOCKERHUB_USERNAME='griefed'

.gitlab/readme_template

-[![$GITHUB_REPONAME](img/$GITHUB_REPONAME_header.png)](https://github.com/$CREATOR_USERNAME/$CREATOR_REPONAME)
+[![$GITHUB_REPONAME](img/$GITHUB_REPONAME_HEADER)](https://github.com/$CREATOR_USERNAME/$CREATOR_REPONAME)
 
 ---
 
@@ -13,7 +13,7 @@ $GITHUB_REPONAME
 
 $DESCRIPTION
 
-[![$CREATOR_REPONAME](img/$GITHUB_REPONAME_screenshot.png)](https://github.com/$CREATOR_USERNAME/$CREATOR_REPONAME)
+[![$CREATOR_REPONAME](img/$GITHUB_REPONAME_SCREENSHOT)](https://github.com/$CREATOR_USERNAME/$CREATOR_REPONAME)
 
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