py3: don't use dict.iterkeys() in hgext/fastannotate/context.py

dict.iterkeys() is not present on Python 3.

Differential Revision: https://phab.mercurial-scm.org/D4431

hgext/fastannotate/context.py

@@ -133,7 +133,7 b' def encodedir(path):'
 def hashdiffopts(diffopts):
     diffoptstr = str(sorted(
         (k, getattr(diffopts, k))
-        for k in mdiff.diffopts.defaults.iterkeys()
+        for k in mdiff.diffopts.defaults
     ))
     return hashlib.sha1(diffoptstr).hexdigest()[:6]