SLING-6186 - Add support for checking code coverage with jacoco

* allow the jacoco version to be configurable; also downgraded to 0.7.6

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk/bundles/scripting/sightly/java-compiler@1767517 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/pom.xml b/pom.xml
index a522534..19168bc 100644
--- a/pom.xml
+++ b/pom.xml
@@ -48,7 +48,7 @@
     </scm>
 
     <properties>
-        <sling.java.version>7</sling.java.version>
+        <jacoco.maven.plugin.version>0.7.6.201602180812</jacoco.maven.plugin.version>
     </properties>
 
     <!-- ======================================================================= -->
@@ -121,7 +121,7 @@
                     <plugin>
                         <groupId>org.jacoco</groupId>
                         <artifactId>jacoco-maven-plugin</artifactId>
-                        <version>0.7.7.201606060606</version>
+                        <version>${jacoco.maven.plugin.version}</version>
                         <executions>
                             <execution>
                                 <id>default-prepare-agent</id>