docs: update calendar, add news item and link release notes for 18.3.1

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>

docs/index.html

@@ -15,6 +15,12 @@
 <div class="content">
 
 <h1>News</h1>
+<h2>December 11, 2018</h2>
+<p>
+<a href="relnotes/18.3.1.html">Mesa 18.3.1</a> is released.
+This is a bug-fix release.
+</p>
+
 <h2>December 7, 2018</h2>
 <p>
 <a href="relnotes/18.3.0.html">Mesa 18.3.0</a> is released.  This is a

docs/release-calendar.html

@@ -53,26 +53,26 @@ if you'd like to nominate a patch in the next stable release.
 </tr>
 <td rowspan="4">18.3</td>
 <td>2018-12-19</td>
-<td>18.3.1</td>
+<td>18.3.2</td>
 <td>Emil Velikov</td>
 <td></td>
 </tr>
 <tr>
 <td>2019-01-09</td>
-<td>18.3.2</td>
-<td>Emil Velikov</td>
-<td/>
-</tr>
-<tr>
-<td>2019-01-23</td>
 <td>18.3.3</td>
 <td>Emil Velikov</td>
 <td/>
 </tr>
 <tr>
-<td>2019-02-06</td>
+<td>2019-01-23</td>
 <td>18.3.4</td>
 <td>Emil Velikov</td>
+<td/>
+</tr>
+<tr>
+<td>2019-02-06</td>
+<td>18.3.5</td>
+<td>Emil Velikov</td>
 </tr>
 </table>
 

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/18.3.1.html">18.3.1 release notes</a>
 <li><a href="relnotes/18.3.0.html">18.3.0 release notes</a>
 <li><a href="relnotes/18.2.6.html">18.2.6 release notes</a>
 <li><a href="relnotes/18.2.5.html">18.2.5 release notes</a>