templates: fix missed space between instability labels

mercurial/templates/map-cmdline.default

@@ -82,5 +82,6 b' labelcset(expr) = label(separate(" ",'
                                  "changeset.{phase}",
                                  if(obsolete, "changeset.obsolete"),
                                  if(instabilities, "changeset.unstable"),
-                                 instabilities % "instability.{instability}"),
+                                 join(instabilities
+                                      % "instability.{instability}", " ")),
                         expr)