help: correct signature of separate() template function stable

help: correct signature of separate() template function

Without the dots, it looked as if separate() would take a list of arguments.

--- a/mercurial/templatefuncs.py	Fri May 18 21:32:05 2018 +0900
+++ b/mercurial/templatefuncs.py	Thu May 24 21:54:31 2018 +0900
@@ -555,7 +555,7 @@
 
     return minirst.format(text, style=style, keep=['verbose'])
 
-@templatefunc('separate(sep, args)', argspec='sep *args')
+@templatefunc('separate(sep, args...)', argspec='sep *args')
 def separate(context, mapping, args):
     """Add a separator between non-empty arguments."""
     if 'sep' not in args: