Update bundled LDAP plugin in order to restore missing help files

In e91782e7 some help files were removed
from core because they were moved to LDAP plugin.
Unfortunately, these help files are not available in LDAP plugin
versions prior to 1.11.
(cherry picked from commit 824662a8)

war/pom.xml

@@ -322,7 +322,7 @@ THE SOFTWARE.
                 <artifactItem>
                   <groupId>org.jenkins-ci.plugins</groupId>
                   <artifactId>ldap</artifactId>
-                  <version>1.6</version>
+                  <version>1.11</version>
                   <type>hpi</type>
                 </artifactItem>
                 <artifactItem>