Fix link to Starlark rules tutorial on the sidebar.
Fixes
<h3>Rules and Macros</h3>
<ul class="sidebar-nav">
<li><a href="/versions/{{ current_version }}/rules.html">Understanding Rules</a></li>
- <li><a href="/versions/{{ current_version }}/rules-tutorial.html">Writing Rules</a></li>
+ <li><a href="/versions/{{ current_version }}/skylark/rules-tutorial.html">Writing Rules</a></li>
<li><a href="/versions/{{ current_version }}/rule-challenges.html">Rules Challenges</a></li>
<li><a href="/versions/{{ current_version }}/skylark/tutorial-creating-a-macro.html">Creating a Macro</a></li>
<li><a href="/versions/{{ current_version }}/skylark/tutorial-custom-verbs.html">Creating Custom Verbs</a></li>
