fsmonitor: fix silly "*kwargs" bug in merge.update() override

Everyone knows that it's supposed to be spelled with two asterisks.

It started failing in fad5e299cfc7 (update: accept --merge to allow
merging across topo branches (issue5125), 2017-02-13) because until
then there was only one argument that was covered by the kwargs, so
*kwargs or **kwargs both worked (or at least that's what I think with
my limited understanding of Python).

hgext/fsmonitor/__init__.py

@@ -669,7 +669,7 b' def wrapupdate(orig, repo, node, branchm'
     with state_update(repo, node, distance, partial):
         return orig(
             repo, node, branchmerge, force, ancestor, mergeancestor,
-            labels, matcher, *kwargs)
+            labels, matcher, **kwargs)
 
 def reposetup(ui, repo):
     # We don't work with largefiles or inotify