Use source/target of Java 8 to avoid default 1.5

Author: headius

gem-assembly-descriptors/src/it/assemble-project-with-gems/java-world/pom.xml

@@ -6,4 +6,16 @@
   <packaging>jar</packaging>
   <version>0.0.0</version>
   <name>java-world</name>
+  <build>
+    <plugins>
+      <plugin>
+        <artifactId>maven-compiler-plugin</artifactId>
+        <version>3.1</version>
+        <configuration>
+          <source>8</source>
+          <target>8</target>
+        </configuration>
+      </plugin>
+    </plugins>
+  </build>
 </project>