Update Maven JAR plugins

Seems to fix the build stalls observed under some builds of the
Java 7 JRE.

Change-Id: I94d5e927b5b2ec3971e9a70c18966368a61ec14c

pom.xml

@@ -216,7 +216,7 @@
         <plugin>
           <groupId>org.apache.maven.plugins</groupId>
           <artifactId>maven-jar-plugin</artifactId>
-          <version>2.4</version>
+          <version>2.5</version>
           <configuration>
             <archive>
               <manifestEntries>
@@ -264,7 +264,7 @@
         <plugin>
           <groupId>org.apache.maven.plugins</groupId>
           <artifactId>maven-source-plugin</artifactId>
-          <version>2.2.1</version>
+          <version>2.3</version>
         </plugin>
 
         <plugin>