Merge branch 'stable-5.4'

Merge branch 'stable-5.4'

* stable-5.4:
  Prepare 5.4.2-SNAPSHOT builds
  JGit v5.4.1.201908211225-r
  Prepare 5.3.4-SNAPSHOT builds
  JGit v5.3.3.201908210735-r
  Add missing @since tag on FileTreeIterator#getLastModifiedInstant
  Prepare 5.1.10-SNAPSHOT builds
  JGit v5.1.9.201908210455-r
  Avoid sign extension when comparing mtime with Instant#getEpochSecond
  Fix deprecation in DirCache caused by Instant based DirCacheEntry

Change-Id: I63156d6b73044d5d8820869a397a0aa94e607b50
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>