fix: pom.xml to reduce vulnerabilities (#16)

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JAVA-ORGAPACHEMAVENSHARED-570592

pom.xml

@@ -288,7 +288,7 @@
                     </goals>
                   </pluginExecutionFilter>
                   <action>
-                    <ignore />
+                    <ignore/>
                   </action>
                 </pluginExecution>
               </pluginExecutions>
@@ -486,7 +486,7 @@
     <maven-surefire-plugin.version>3.0.0-M3</maven-surefire-plugin.version>
     <maven-surefire-report-plugin.version>3.0.0-M3</maven-surefire-report-plugin.version>
     <maven-toolchains-plugin.version>1.1</maven-toolchains-plugin.version>
-    <maven.version>3.6.1</maven.version>
+    <maven.version>3.8.2</maven.version>
     <nexus-staging-maven-plugin.version>1.6.8</nexus-staging-maven-plugin.version>
     <!-- Properties for maven-compiler-plugin -->
     <maven.compiler.compilerVersion>1.8</maven.compiler.compilerVersion>