Bump spring-framework-bom from 5.1.6.RELEASE to 5.1.18.RELEASE

Bumps [spring-framework-bom](https://github.com/spring-projects/spring-framework) from 5.1.6.RELEASE to 5.1.18.RELEASE.
- [Release notes](https://github.com/spring-projects/spring-framework/releases)
- [Commits](spring-projects/spring-framework@v5.1.6.RELEASE...v5.1.18.RELEASE)

---
updated-dependencies:
- dependency-name: org.springframework:spring-framework-bom
  dependency-type: direct:production
...

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

pom.xml

@@ -88,7 +88,7 @@
 		<junit-jupiter.version>5.4.1</junit-jupiter.version>
 		<mockito.version>3.0.0</mockito.version>
 		<slf4j.version>1.7.26</slf4j.version>
-		<spring.version>5.1.6.RELEASE</spring.version>
+		<spring.version>5.1.18.RELEASE</spring.version>
 
 		<!-- Maven plugins -->
 		<ant-contrib.version>1.0b3</ant-contrib.version>