PDFBOX-4071: move maven-enforcer-plugin to pluginManagement section so that it has an effect on subprojects; require maven 3.5
PDFBOX-4071: move maven-enforcer-plugin to pluginManagement section so that it has an effect on subprojects; require maven 3.5

git-svn-id: c3ad59981690829a43dc34c293c4e2cd04bcd994@1853272 13f79535-47bb-0310-9956-ffa450edef68

apache/pdfbox,kalaspuffar/pdfbox,apache/pdfbox,kalaspuffar/pdfbox