make compiler.target/source as a property so we can override those with the command line

Signed-off-by: olivier lamy <oliver.lamy@gmail.com>

pom.xml

@@ -14,6 +14,8 @@
   <inceptionYear>1995</inceptionYear>
 
   <properties>
+    <compiler.source>1.8</compiler.source>
+    <compiler.target>1.8</compiler.target>
     <jetty.url>http://www.eclipse.org/jetty</jetty.url>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     <build-support.version>1.4</build-support.version>
@@ -438,8 +440,8 @@
           <artifactId>maven-compiler-plugin</artifactId>
           <version>${maven.compiler.plugin.version}</version>
           <configuration>
-            <source>1.8</source>
-            <target>1.8</target>
+            <source>${compiler.source}</source>
+            <target>${compiler.target}</target>
           </configuration>
         </plugin>
         <plugin>