Update checkstyle version due to CVE-2019-9658

Author: joshiste

pom.xml

@@ -61,7 +61,7 @@
         <git-commit-id-plugin.version>2.2.4</git-commit-id-plugin.version>
         <flatten-maven-plugin.version>1.0.1</flatten-maven-plugin.version>
         <maven-checkstyle-plugin.version>3.0.0</maven-checkstyle-plugin.version>
-        <checkstyle.version>8.8</checkstyle.version>
+        <checkstyle.version>8.18</checkstyle.version>
         <nexus-staging-maven-plugin.version>1.6.8</nexus-staging-maven-plugin.version>
     </properties>
     <modules>