Use jenkins.baseline to reduce bom update mistakes (#96)

pom.xml

@@ -33,7 +33,9 @@
         <changelist>999999-SNAPSHOT</changelist>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <argLine>-Dfile.encoding=${project.build.sourceEncoding}</argLine>
-        <jenkins.version>2.426.3</jenkins.version>
+        <!-- https://www.jenkins.io/doc/developer/plugin-development/choosing-jenkins-baseline/ -->
+        <jenkins.baseline>2.426</jenkins.baseline>
+        <jenkins.version>${jenkins.baseline}.3</jenkins.version>
         <spotbugs.effort>Max</spotbugs.effort>
         <spotbugs.failOnError>true</spotbugs.failOnError>
         <spotbugs.threshold>Medium</spotbugs.threshold>
@@ -43,7 +45,7 @@
         <dependencies>
             <dependency>
                 <groupId>io.jenkins.tools.bom</groupId>
-                <artifactId>bom-2.426.x</artifactId>
+                <artifactId>bom-${jenkins.baseline}.x</artifactId>
                 <version>3208.vb_21177d4b_cd9</version>
                 <type>pom</type>
                 <scope>import</scope>