awesomerc: allow 'false' in floatapps

Signed-off-by: koniu <gkusnierz@gmail.com>
Signed-off-by: Julien Danjou <julien@danjou.info>

awesomerc.lua.in

@@ -375,9 +375,9 @@ awful.hooks.manage.register(function (c, startup)
     -- Check if the application should be floating.
     local cls = c.class
     local inst = c.instance
-    if floatapps[cls] then
+    if floatapps[cls] ~= nil then
         awful.client.floating.set(c, floatapps[cls])
-    elseif floatapps[inst] then
+    elseif floatapps[inst] ~= nil then
         awful.client.floating.set(c, floatapps[inst])
     end