Added version enforcement for maven-compiler-plugin, per mvn requirements

Author: GreyCat

pom.xml

@@ -114,6 +114,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-compiler-plugin</artifactId>
+        <version>3.1</version>
         <configuration>
           <source>6</source>
           <target>6</target>