Update pom.xml with JDK 16.

Author: jmrozanec

pom.xml

@@ -176,8 +176,8 @@
                 <artifactId>maven-compiler-plugin</artifactId>
                 <version>3.8.1</version>
                 <configuration>
-                    <source>17</source>
-                    <target>17</target>
+                    <source>16</source>
+                    <target>16</target>
                     <compilerArgs>
                         <arg>-J--add-opens=jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED</arg>
                         <arg>-J--add-opens=jdk.compiler/com.sun.tools.javac.comp=ALL-UNNAMED</arg>