Repo header: Fix DOIReg variable capitalisation

templates/repo/header.tmpl

@@ -33,7 +33,7 @@
 									</a>
 								</div>
 							{{end}}
-							{{if not $.DoiReg}}
+							{{if not $.DOIReg}}
 								{{if and (and $.DOI $.IsRepositoryAdmin) (not .IsPrivate)}}
 								<div class="ui labeled button" tabindex="0">
 									<a class="ui basic button"