Upgrade Maven to 3.9.11. Prerequisites still 3.6.3
diff --git a/pom.xml b/pom.xml
index 240e683..0557062 100644
--- a/pom.xml
+++ b/pom.xml
@@ -37,7 +37,7 @@
   <inceptionYear>2016</inceptionYear>
 
   <prerequisites>
-    <maven>${mavenVersion}</maven>
+    <maven>3.6.3</maven>
   </prerequisites>
 
   <scm>
@@ -62,7 +62,7 @@
   </distributionManagement>
 
   <properties>
-    <mavenVersion>3.6.3</mavenVersion>
+    <mavenVersion>3.9.11</mavenVersion>
     <project.build.outputTimestamp>2021-02-24T19:52:25Z</project.build.outputTimestamp>
 
     <version.maven-invoker-plugin>3.9.1</version.maven-invoker-plugin>