Update CONTRIBUTING.md (#4277)

The build no longer works with Maven 3.5.3.  If you try it, you end up with this:

[INFO] --- maven-enforcer-plugin:3.0.0-M2:enforce (display-info) @ jenkins-parent ---
[WARNING] Rule 0: org.apache.maven.plugins.enforcer.RequireMavenVersion failed with message:
3.5.4+ required to use Incrementals.
[INFO] ------------------------------------------------------------------------
[INFO] Reactor Summary:
[INFO] 
[INFO] Jenkins main module 2.199-SNAPSHOT ................. FAILURE [ 44.098 s]

CONTRIBUTING.md

@@ -13,7 +13,7 @@ This page provides information about contributing code to the Jenkins core codeb
      - In Jenkins project we usually use [OpenJDK],
   but you can use other JDKs as well.
      - Java 9+ is **not supported** in Jenkins.
-  * Maven 3.5.3 or above. You can [download maven].
+  * Maven 3.5.4 or above. You can [download maven].
   * Any IDE which supports importing Maven projects.
 4. Setup your development environment as described in [Preparing for Plugin Development]
 
@@ -128,4 +128,4 @@ just submit a pull request.
 [Jenkins Security Team]: https://jenkins.io/security/#team
 [ci.jenkins.io]: https://ci.jenkins.io/
 [Jenkins Pipeline]: https://jenkins.io/doc/book/pipeline/
-[Jenkinsfile]: ./Jenkinsfile
+[Jenkinsfile]: ./Jenkinsfile