correct date format

config/common.conf

@@ -17,7 +17,7 @@ DISTDIR="/usr/portage/distfiles"
 # Using this, the default tarball and image date format can be changed according to the
 # requirement. This customizable format may be needed when you want to set different
 # timestamp in output files. This option can be overridden by using -D option.
-TARBALLDATE="%Y%m"
+TARBALLDATE="%Y-%m"
 
 # This option specifies a compression algorithm that will be used to produce any tarball
 # images, including stages as well as Portage snapshots. Actually supported: bz2, gz, xz.