YETUS-319 correct contributing sub-page links.

* make header point to contribute/

  when hosted by an ASF web server, leaving it off automatically
  redirects to include the trailing slash, but in 'bundle exec middleman'
  mode it does not, which changes the root for relative urls.

* update contribute page to leave 'contribute/' off relative path

  when page is viewed with trailing /, that part of the path is assumed.

Signed-off-by: Allen Wittenauer <aw@apache.org>
diff --git a/asf-site-src/source/_header.md.erb b/asf-site-src/source/_header.md.erb
index a9609ed..b624ca3 100644
--- a/asf-site-src/source/_header.md.erb
+++ b/asf-site-src/source/_header.md.erb
@@ -56,7 +56,7 @@
                         </li>
                         <li role="presentation"><a role="menuitem" tabindex="-1" href="https://github.com/apache/yetus"><i class="fa fa-github-alt"></i> Source (GitHub)</a>
                         </li>
-                        <li role="presentation"><a role="menuitem" tabindex="-1" href="/contribute"><i class="fa fa-code-fork"></i> Contributing</a>
+                        <li role="presentation"><a role="menuitem" tabindex="-1" href="/contribute/"><i class="fa fa-code-fork"></i> Contributing</a>
                         </li>
                         <li role="presentation"><a role="menuitem" tabindex="-1" href="https://twitter.com/ApacheYetus"><i class="fa fa-twitter"></i> @ApacheYetus</a>
                         </li>
diff --git a/asf-site-src/source/contribute.html.md b/asf-site-src/source/contribute.html.md
index cce81f4..ecd8689 100644
--- a/asf-site-src/source/contribute.html.md
+++ b/asf-site-src/source/contribute.html.md
@@ -41,5 +41,5 @@
 
 Below are guides meant to give you help accomplishing specific tasks for the project:
 
-   * [Maintaining the Yetus Website](contribute/website) - walks through how to view the website locally, update various static and generated pages, and render the html for publishing.
-   * [Working with Release Candiates](contribute/releases) - covers managing the release process, validating proposed release candidates, and publishing project approved artifacts.
+   * [Maintaining the Yetus Website](website) - walks through how to view the website locally, update various static and generated pages, and render the html for publishing.
+   * [Working with Release Candiates](releases) - covers managing the release process, validating proposed release candidates, and publishing project approved artifacts.