fix(init): increment the default timeout to 15 seconds

On slow devices (for example Android smartphones using Termux), loading
a lot of org files takes more than 5 seconds, which will make the
default timeout for the promise to expire, leaving the plugin in a
semi-loaded state where some functionalities may not work, forcing the
user to reload the plugin multiple times hoping that the system has
something already cached and it will take less than 5 seconds.

lua/orgmode/init.lua

@@ -50,7 +50,7 @@ function Org:init()
     :new({
       paths = require('orgmode.config').org_agenda_files,
     })
-    :load_sync()
+    :load_sync(true, 20000)
   self.agenda = require('orgmode.agenda'):new({
     files = self.files,
   })