how to use mbstring on heroku 28php 29

1Create Composer file in your app folder
2
3project_dir:~$> touch composer.json
4
5# add these lines in your composer.json
6{
7  "require": {
8    "ext-mbstring": "*"
9  }
10}
11
12#save composer file
13#And heroku will automatically add the mbstring extension 
14#to your app on the next deploy.