Fix notification docs to use proper utils function.

Author: kristijanhusak

DOCS.md

@@ -733,7 +733,7 @@ require('orgmode').setup({
     notifier = function(tasks)
       local result = {}
       for _, task in ipairs(tasks) do
-        utils.concat(result, {
+        require('orgmode.utils').concat(result, {
           string.format('# %s (%s)', task.category, task.humanized_duration),
           string.format('%s %s %s', string.rep('*', task.level), task.todo, task.title),
           string.format('%s: <%s>', task.type, task.time:to_string())

doc/orgmode.txt

@@ -967,7 +967,7 @@ Default configuration (detailed description below):
         notifier = function(tasks)
           local result = {}
           for _, task in ipairs(tasks) do
-            utils.concat(result, {
+            require('orgmode.utils').concat(result, {
               string.format('# %s (%s)', task.category, task.humanized_duration),
               string.format('%s %s %s', string.rep('*', task.level), task.todo, task.title),
               string.format('%s: <%s>', task.type, task.time:to_string())