Update checkstyle (CVE-2019-9658) (#1073)

diff --git a/pom.xml b/pom.xml
index bcf4d47..13ab2f4 100644
--- a/pom.xml
+++ b/pom.xml
@@ -174,7 +174,7 @@
             <dependency>
               <groupId>com.puppycrawl.tools</groupId>
               <artifactId>checkstyle</artifactId>
-              <version>8.14</version>
+              <version>8.18</version>
             </dependency>
             <dependency>
               <groupId>org.apache.fluo</groupId>