Rails apps with version 4 or above has some files under the
bin folder namely
spring. But since I had
bin folder gitignored, these files dint make it to heroku.
To fix this:
Remove bin from ~/.gitignore
bundle install or
Commit your changes with
git add . and
git commit -m "Add bin back"
Push your changes to Heroku with git push heroku master
Heroku has a detailed article on the same which can be found here.