Bump spring-core from 5.2.7.RELEASE to 5.3.18

Bumps [spring-core](https://github.com/spring-projects/spring-framework) from 5.2.7.RELEASE to 5.3.18.
- [Release notes](https://github.com/spring-projects/spring-framework/releases)
- [Commits](spring-projects/spring-framework@v5.2.7.RELEASE...v5.3.18)

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

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

Author: dependabot[bot]

pom.xml

@@ -7,7 +7,7 @@
   <packaging>war</packaging>
   <name>A rapid tileserver using JNI bindings against mapnik 3.0.x</name>
   <properties>
-    <spring.version>5.2.7.RELEASE</spring.version>
+    <spring.version>5.3.18</spring.version>
     <geotools.version>20.0</geotools.version>
   </properties>
   <build>