Fix project links for multilingual sites

Use `relLangURL` rather than `relURL` for project links.

See #442

layouts/partials/publication_links.html

@@ -31,7 +31,7 @@
 {{ end }}
 {{ if $.Params.projects }}
 {{ range $.Params.projects }}
-<a class="btn btn-primary btn-outline{{ if $is_list }} btn-xs{{end}}" href="{{ printf "project/%s/" . | relURL }}">
+<a class="btn btn-primary btn-outline{{ if $is_list }} btn-xs{{end}}" href="{{ printf "project/%s/" . | relLangURL }}">
   {{ i18n "btn_project" }}
 </a>
 {{ end }}

layouts/partials/talk_links.html

@@ -22,7 +22,7 @@
 </a>
 {{ end }}
 {{ range $.Params.projects }}
-<a class="btn btn-primary btn-outline{{ if $is_list }} btn-xs{{end}}" href="{{ printf "project/%s/" . | relURL }}">
+<a class="btn btn-primary btn-outline{{ if $is_list }} btn-xs{{end}}" href="{{ printf "project/%s/" . | relLangURL }}">
   {{ i18n "btn_project" }}
 </a>
 {{ end }}