Bump tomcatVersion from 11.0.15 to 11.0.18

Bumps `tomcatVersion` from 11.0.15 to 11.0.18.

Updates `org.apache.tomcat.embed:tomcat-embed-core` from 11.0.15 to 11.0.18

Updates `org.apache.tomcat.embed:tomcat-embed-jasper` from 11.0.15 to 11.0.18

---
updated-dependencies:
- dependency-name: org.apache.tomcat.embed:tomcat-embed-core
  dependency-version: 11.0.18
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.apache.tomcat.embed:tomcat-embed-jasper
  dependency-version: 11.0.18
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

example-09-dispatcher-servlet/build.gradle

@@ -11,7 +11,7 @@ buildscript {
 apply plugin: "com.bmuschko.tomcat"
 
 dependencies {
-    def tomcatVersion = "11.0.15"
+    def tomcatVersion = "11.0.18"
 
     tomcat("org.apache.tomcat.embed:tomcat-embed-core:${tomcatVersion}")
     tomcat("org.apache.tomcat.embed:tomcat-embed-jasper:${tomcatVersion}")

example-10-spring-mvc/build.gradle

@@ -11,7 +11,7 @@ buildscript {
 apply plugin: "com.bmuschko.tomcat"
 
 dependencies {
-    def tomcatVersion = "11.0.15"
+    def tomcatVersion = "11.0.18"
 
     tomcat("org.apache.tomcat.embed:tomcat-embed-core:${tomcatVersion}")
     tomcat("org.apache.tomcat.embed:tomcat-embed-jasper:${tomcatVersion}")