array in yml is read as string on Heroku #24

Hi,
I put array in yml file and it works just fine on my local test machine.

ad_sequence1: [z,z,z,z,z,z,z,z,z,z]
ad_sequence2: ["z","z","z","z","z","z","z","z","z","z"]

but if I deploy the code on heroku, in a sudden it is recognized as string as below:

["z,z,z,z,z,z,z,z,z,z"]
or
'["z","z","z","z","z","z","z","z","z","z"]'

Can someone please enlighten me?