Bump spring-core from 5.3.12 to 5.3.18

Bumps [spring-core](https://github.com/spring-projects/spring-framework) from 5.3.12 to 5.3.18.
- [Release notes](https://github.com/spring-projects/spring-framework/releases)
- [Commits](https://github.com/spring-projects/spring-framework/compare/v5.3.12...v5.3.18)

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

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

pom.xml

@@ -53,7 +53,7 @@
         <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
         <curator.version>4.3.0</curator.version>
         <zookeeper.version>3.4.14</zookeeper.version>
-        <spring.version>5.3.12</spring.version>
+        <spring.version>5.3.18</spring.version>
         <spring.boot.version>2.5.6</spring.boot.version>
         <java.version>1.8</java.version>
         <logback.version>1.2.3</logback.version>