Fix the default config

When I cherry-picked commit 2785d695ce from master, I didn't notice that it uses
connect_signal() which is add_signal() in 3.4-land. That was half a month ago.
Since then, no one complaint about this, so no one hit the problem yet?

Ok, it is in the default config which I guess isn't what the people who use
git/3.4 run. Still, would have been nice to know that people actually test the
mess which I produce. :-(

Signed-off-by: Uli Schlachter <psychon@znc.in>

awesomerc.lua.in

@@ -19,7 +19,7 @@ end
 -- Handle runtime errors after startup
 do
     local in_error = false
-    awesome.connect_signal("debug::error", function (err)
+    awesome.add_signal("debug::error", function (err)
         -- Make sure we don't go into an endless error loop
         if in_error then return end
         in_error = true