Fix a typo in a help text

See !200 (merged)

package-source-builder/overlay/usr/bin/apertis-pkg-merge-upstream-to-downstreams

@@ -83,7 +83,7 @@ def main():
   parser.add_argument('--local-version-suffix', dest="local_suffix", type=str, default="apertis", help='the local version suffix to be used in new changelog entries')
   parser.add_argument('project_url', type=str, help='git project url to push updates to')
   parser.add_argument('--auto-merge', dest='auto_merge', type=str, default='',
-                      help='list of branches that allow auto merg, colon seperate (e.g.  apertis/v2020dev0:apertis/v2019)')
+                      help='list of branches that allow auto merge, colon-separated (e.g.  apertis/v2020dev0:apertis/v2019)')
   args = parser.parse_args()
 
   upstream = args.upstream