Add Implementation-Version to manifest

The Impelmentation-Version is needed by Gerrit to display version info
in the gerrit plugin ssh commands and the upcoming web UI.  Hopefully in
the future Gerrit can alert of new versions of plugins/auto-update as
well.

Signed-off-by: Brad Larson <bklarson@gmail.com>
Change-Id: I17be930098e21ae7d1d78382b68ef7103e41eccd

pom.xml

diff --git a/pom.xml b/pom.xml
index 79f0210..cb14b14 100644
--- a/pom.xml
+++ b/pom.xml
@@ -53,6 +53,7 @@
               <Gerrit-Plugin>helloworld</Gerrit-Plugin>
               <Gerrit-SshModule>com.google.gerrit.plugins.HelloWorldCommandModule</Gerrit-SshModule>
               <Gerrit-Version>${gerrit-version}</Gerrit-Version>
+              <Implementation-Version>${project.version}</Implementation-Version>
             </manifestEntries>
           </archive>
         </configuration>