docs: update calendar 18.2.0-rc1 and 18.2.0-rc2 are out

Signed-off-by: Andres Gomez <agomez@igalia.com>

docs/release-calendar.html

@@ -52,19 +52,7 @@ if you'd like to nominate a patch in the next stable release.
 <td>Last planned 18.1.x release</td>
 </tr>
 <tr>
-<td rowspan="4">18.2</td>
-<td>2018-08-01</td>
-<td>18.2.0rc1</td>
-<td>Andres Gomez</td>
-<td></td>
-</tr>
-<tr>
-<td>2018-08-08</td>
-<td>18.2.0rc2</td>
-<td>Andres Gomez</td>
-<td></td>
-</tr>
-<tr>
+<td rowspan="2">18.2</td>
 <td>2018-08-15</td>
 <td>18.2.0rc3</td>
 <td>Andres Gomez</td>