Use jenkins.baseline to reduce bom update mistakes (#38)

Author: strangelookingnerd

pom.xml

@@ -38,7 +38,8 @@
     <gitHubRepo>jenkinsci/${project.artifactId}-plugin</gitHubRepo>
 
     <!-- https://www.jenkins.io/doc/developer/plugin-development/choosing-jenkins-baseline/ -->
-    <jenkins.version>2.426.3</jenkins.version>
+    <jenkins.baseline>2.426</jenkins.baseline>
+    <jenkins.version>${jenkins.baseline}.3</jenkins.version>
     <maven.version>3.8.1</maven.version>
     <revision>1.0</revision>
     <spotless.check.skip>false</spotless.check.skip>
@@ -49,7 +50,7 @@
       <dependency>
         <!-- Pick up common dependencies for the selected LTS line: https://github.com/jenkinsci/bom#usage -->
         <groupId>io.jenkins.tools.bom</groupId>
-        <artifactId>bom-2.426.x</artifactId>
+        <artifactId>bom-${jenkins.baseline}.x</artifactId>
         <version>2928.ved44ea_84e034</version>
         <type>pom</type>
         <scope>import</scope>