[JENKINS-50969] Bump to latest maven-site-plugin

[batmat]

Apply a more global bump like in jenkinsci/jenkins#3408

@reviewbybees esp. @daniel-beck

See JENKINS-50969.

[oleg-nenashev]

Would be nice to have a full changelog link so that it can be referenced

[batmat]

I guess you mean the changelog for maven-site-plugin 3.6..3.7 ?

[oleg-nenashev]

Yes, preferably in human-readable format (if there is such page somewhere)

[batmat]

Best I could find is https://lists.apache.org/list.html?announce@maven.apache.org:2017-12

Release Notes - Maven Site Plugin - Version 3.7

** Bug

• [MSITE-796] - Unable to generate site with JDK9 -
  java.lang.ExceptionInInitializerError / Caused by:
  java.lang.StringIndexOutOfBoundsException: begin 0, end 3, length 1

** Improvement

• [MSITE-787] - display what reports are added automatically when no
  reportSet is defined
• [MSITE-791] - upgrade Doxia to 1.8 to benefit from new Markdown parser
  (require Java 7)
• [MSITE-797] - simplify stacktrace in case of report plugin execution
  failure
• [MSITE-804] - update Doxia Site Renderer to 1.8

** Task

• [MSITE-792] - drop reportPlugins parameter ("new format")
• [MSITE-802] - Support more than one directory: improve target/generated-
  site documentation
• [MSITE-805] - switch to Git