Upgraded Apache Ant

Turns out there was a security advisory posted on Ant 1.8.3
(http://ant.apache.org/security.html) though the affected code is not
used in Jenkins.

Reference: http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2012-2098

pom.xml

@@ -132,7 +132,7 @@ THE SOFTWARE.
       <dependency>
         <groupId>org.apache.ant</groupId>
         <artifactId>ant</artifactId>
-        <version>1.8.3</version>
+        <version>1.8.4</version>
       </dependency>
 
       <dependency>