histedit, i18n: replace '+' with concatenation to make hggettext happy

hgext/histedit.py

@@ -570,7 +570,7 b' def _histedit(ui, repo, *freeargs, **opt'
         else:
             rootrevs = list(repo.set('roots(%lr)', revs))
             if len(rootrevs) != 1:
-                raise util.Abort(_('The specified revisions must have ' +
+                raise util.Abort(_('The specified revisions must have '
                     'exactly one common root'))
             root = rootrevs[0].node()