Fix no github_users titling in repositories.md (#2647)

Inverted order of title and {% if site.data.repositories.github_users
%}, so that if there is no github_users, the "GitHub users" title does
not appear.

_pages/repositories.md

@@ -7,10 +7,10 @@ nav: true
 nav_order: 4
 ---
 
-## GitHub users
-
 {% if site.data.repositories.github_users %}
 
+## GitHub users
+
 <div class="repositories d-flex flex-wrap flex-md-row flex-column justify-content-between align-items-center">
   {% for user in site.data.repositories.github_users %}
     {% include repository/repo_user.liquid username=user %}
@@ -35,10 +35,10 @@ nav_order: 4
 {% endif %}
 {% endif %}
 
-## GitHub Repositories
-
 {% if site.data.repositories.github_repos %}
 
+## GitHub Repositories
+
 <div class="repositories d-flex flex-wrap flex-md-row flex-column justify-content-between align-items-center">
   {% for repo in site.data.repositories.github_repos %}
     {% include repository/repo.liquid repository=repo %}