Update pom.xml

Author: Ranjan Dasgupta

pom.xml

@@ -10,6 +10,9 @@
         <!-- source & target java version for MQTT Client -->
         <maven.compiler.source>1.8</maven.compiler.source>
         <maven.compiler.target>1.8</maven.compiler.target>
+        <mqttclient.java.version>1.8</mqttclient.java.version>
+        <!-- source & target java version for others modules -->
+        <java.version>1.8</java.version>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <build.level>${maven.build.timestamp}</build.level>
         <tycho.version>1.7.0</tycho.version>