Use javac --release instead of -source & -target

`--release` also verifies that only API from that Java version is used.
Otherwise when building with a JDK newer than the target version it would
be possible to accidentally use API not available in the target version.

Author: Marcono1234

pom.xml

@@ -131,8 +131,7 @@
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-compiler-plugin</artifactId>
                 <configuration>
-                    <source>${java.target}</source>
-                    <target>${java.target}</target>
+                    <release>${java.target}</release>
                     <compilerArgument>-Xlint:deprecation</compilerArgument>
                 </configuration>
             </plugin>