Error while running playbook

ERROR! Syntax Error while loading YAML.
could not find expected ‘:’

The error appears to have been in ‘/home/ansible/LAMP/site.yml’: line 9, column 3, but may
be elsewhere in the file depending on the exact syntax problem.

The offending line appears to be:

roles:
^ here

i am getting this error while running playbook. As beginner i created a ansible playbook to deploy lamp stack for demo purpose.
Error is about to line indentation i guess but i checked and found it ok.
this is my site.yml

This should be a colon not equal sign.