Bump spring-boot-starter-web in /examples/spring/servlet (#2099)

Bumps [spring-boot-starter-web](https://github.com/spring-projects/spring-boot) from 2.0.5.RELEASE to 2.5.12.
- [Release notes](https://github.com/spring-projects/spring-boot/releases)
- [Commits](spring-projects/spring-boot@v2.0.5.RELEASE...v2.5.12)

---
updated-dependencies:
- dependency-name: org.springframework.boot:spring-boot-starter-web
  dependency-type: direct:production
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

examples/spring/servlet/pom.xml

@@ -15,7 +15,7 @@
     <apachehttp.version>4.1.4</apachehttp.version>
     <opencensus.version>0.26.0</opencensus.version><!-- LATEST_OPENCENSUS_RELEASE_VERSION -->
     <prometheus.version>0.6.0</prometheus.version>
-    <springboot.version>2.0.5.RELEASE</springboot.version>
+    <springboot.version>2.5.12</springboot.version>
     <java.version>1.8</java.version>
   </properties>