Correct reference to "site.salsa_url"

Re. diffoscope#252

index.md

@@ -95,7 +95,7 @@ You can try it now using Docker:
 * <a href="{{ site.salsa_url }}">Git repository</a>
 
 * <a href="{{ site.salsa_url }}/issues">Issues and feature requests</a>
-  * <a href="{{ sals_url }}/issues/new">File a new issue!</a> (<a href="https://reproducible-builds.org/contribute/salsa/">registration instructions</a>)
+  * <a href="{{ site.salsa_url }}/issues/new">File a new issue!</a> (<a href="https://reproducible-builds.org/contribute/salsa/">registration instructions</a>)
 
 * <a href="https://lists.reproducible-builds.org/listinfo/diffoscope">Users and developers mailing-list</a>