webutil: move from dict() construction to {} literals

The latter are both faster and more consistent across Python 2 and 3.

mercurial/hgweb/webutil.py

@@ -146,7 +146,7 b' def children(ctx, hide=None):'
 def renamelink(fctx):
     r = fctx.renamed()
     if r:
-        return [dict(file=r[0], node=hex(r[1]))]
+        return [{'file': r[0], 'node': hex(r[1])}]
     return []
 
 def nodetagsdict(repo, node):