Bump spring.version from 5.1.5.RELEASE to 5.1.6.RELEASE

Bumps `spring.version` from 5.1.5.RELEASE to 5.1.6.RELEASE.

Updates `spring-web` from 5.1.5.RELEASE to 5.1.6.RELEASE
- [Release notes](https://github.com/spring-projects/spring-framework/releases)
- [Commits](spring-projects/spring-framework@v5.1.5.RELEASE...v5.1.6.RELEASE)

Updates `spring-test` from 5.1.5.RELEASE to 5.1.6.RELEASE
- [Release notes](https://github.com/spring-projects/spring-framework/releases)
- [Commits](spring-projects/spring-framework@v5.1.5.RELEASE...v5.1.6.RELEASE)

Updates `spring-webmvc` from 5.1.5.RELEASE to 5.1.6.RELEASE
- [Release notes](https://github.com/spring-projects/spring-framework/releases)
- [Commits](spring-projects/spring-framework@v5.1.5.RELEASE...v5.1.6.RELEASE)

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

pom.xml

@@ -37,7 +37,7 @@
         <maven.compiler.source>1.8</maven.compiler.source>
         <maven.compiler.target>1.8</maven.compiler.target>
 
-        <spring.version>5.1.5.RELEASE</spring.version>
+        <spring.version>5.1.6.RELEASE</spring.version>
         <jackson.version>2.9.8</jackson.version>
     </properties>