docs: update calendar, add new item and link release notes for 18.2.4

Signed-off-by: Juan A. Suarez Romero <jasuarez@igalia.com>

docs/index.html

@@ -15,6 +15,12 @@
 <div class="content">
 
 <h1>News</h1>
+<h2>October 31, 2018</h2>
+<p>
+<a href="relnotes/18.2.4.html">Mesa 18.2.4</a> is released.
+This is a bug-fix release.
+</p>
+
 <h2>October 19, 2018</h2>
 <p>
 <a href="relnotes/18.2.3.html">Mesa 18.2.3</a> is released.

docs/release-calendar.html

@@ -39,13 +39,7 @@ if you'd like to nominate a patch in the next stable release.
 <th>Notes</th>
 </tr>
 <tr>
-<td rowspan="4">18.2</td>
+<td rowspan="3">18.2</td>
-<td>2018-10-31</td>
-<td>18.2.4</td>
-<td>Juan A. Suarez</td>
-<td></td>
-</tr>
-<tr>
 <td>2018-11-14</td>
 <td>18.2.5</td>
 <td>Juan A. Suarez</td>

docs/relnotes.html

@@ -21,6 +21,7 @@ The release notes summarize what's new or changed in each Mesa release.
 </p>
 
 <ul>
+<li><a href="relnotes/18.2.4.html">18.2.4 release notes</a>
 <li><a href="relnotes/18.2.3.html">18.2.3 release notes</a>
 <li><a href="relnotes/18.2.2.html">18.2.2 release notes</a>
 <li><a href="relnotes/18.1.9.html">18.1.9 release notes</a>