add draft for 5.15 release

[Siedlerchr]

TODO: add external contributors

[koppor]

Tried

jbang gcl@koppor/github-contributors-list --startrevision=v5.13 --endrevision=v5.15 --repos

itory=JabRef/jabref .

Got

java.lang.NullPointerException: Cannot invoke "java.lang.Boolean.booleanValue()" because "this.jna" is null
        at org.jline.terminal.TerminalBuilder.doBuild(TerminalBuilder.java:443)
        at org.jline.terminal.TerminalBuilder.build(TerminalBuilder.java:362)
        at me.tongfei.progressbar.TerminalUtils.getTerminal(TerminalUtils.java:83)
        at me.tongfei.progressbar.TerminalUtils.hasCursorMovementSupport(TerminalUtils.java:37)
        at me.tongfei.progressbar.Util.createConsoleConsumer(Util.java:30)
        at me.tongfei.progressbar.Util.createConsoleConsumer(Util.java:26)
        at me.tongfei.progressbar.ProgressBar.<init>(ProgressBar.java:80)
        at me.tongfei.progressbar.ProgressBar.<init>(ProgressBar.java:38)
        at gcl.call(gcl.java:220)

Issue: koppor/github-contributors-list#22