Bump v3 API docs version release-candidate

Author: ari-wg-gitbot

version/release-candidate/index.html

@@ -111,6 +111,10 @@
     <nav class="toc-wrapper">
       <img src="images/logo.png" alt="" />
 
+      <button id="theme-toggle" class="theme-toggle" aria-label="Toggle theme">
+        <span class="theme-icon">☾</span>
+      </button>
+
       <div class="dropdown version-dropdown">
         <button type="button" id="version-dropdown-button" class="version-dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">Release Candidate<span class="caret">&#x25BE;</span></button>