Build: Maven plugin updates

- maven-compiler-plugin ............................. 3.9.0  -> 3.10.0
- maven-pmd-plugin .................................. 3.15.0 -> 3.16.0
- org.sonatype.plugins:nexus-staging-maven-plugin ... 1.6.9  -> 1.6.11

pom.xml

@@ -121,7 +121,7 @@
         <plugin>
           <!-- http://maven.apache.org/plugins/maven-compile-plugin/plugin-info.html -->
           <artifactId>maven-compiler-plugin</artifactId>
-          <version>3.9.0</version>
+          <version>3.10.0</version>
           <configuration>
             <source>1.8</source>
             <target>1.8</target>
@@ -236,7 +236,7 @@
         </plugin>
         <plugin>
           <artifactId>maven-pmd-plugin</artifactId>
-          <version>3.14.0</version>
+          <version>3.16.0</version>
           <configuration>
             <format>html</format>
             <linkXRef>true</linkXRef>
@@ -271,7 +271,7 @@
         <plugin>
           <groupId>org.sonatype.plugins</groupId>
           <artifactId>nexus-staging-maven-plugin</artifactId>
-          <version>1.6.9</version>
+          <version>1.6.11</version>
         </plugin>
         <plugin>
           <artifactId>maven-gpg-plugin</artifactId>