Require Jenkins core 2.440.3 instead of 2.440.1

https://www.jenkins.io/doc/developer/plugin-development/choosing-jenkins-baseline/
recommends Jenkins 2.440.3 rather than 2.440.1.  Let's upgrade the
requirement to 2.440.3 so that the dependabot pull request for BOM can
be merged.

jenkinsci#660 is the
dependabot pull request

pom.xml

@@ -54,7 +54,7 @@
 
   <properties>
     <changelist>999999-SNAPSHOT</changelist>
-    <jenkins.version>2.440.1</jenkins.version>
+    <jenkins.version>2.440.3</jenkins.version>
     <gitHubRepo>jenkinsci/${project.artifactId}-plugin</gitHubRepo>
     <spotbugs.effort>Max</spotbugs.effort>
     <spotbugs.threshold>Low</spotbugs.threshold>