Prepare Jaybird 6.0.0-beta-1 release

Author: mrotteveel

build.properties

@@ -2,6 +2,6 @@ version.major=6
 version.minor=0
 version.revision=0
 # version.tag should start with a dash (-) unless it is empty
-version.tag=-SNAPSHOT
+version.tag=-beta-1
 # This must be set to the git tag for a release, otherwise to the branch
-version.svntag=master
+version.svntag=v6.0.0-beta-1