Reformat stack.yaml

[rcannon]

Stack (>= 1.11) no longer supports this format for specifying extra dependencies to pull from github:

packages
- location:
    git: https://github.com/bitemyapp/esqueleto.git
    commit: 08c9b4cdf977d5bcd1baba046a007940c1940758
  extra-dep: true

See here for details.

[rcannon]

The error thrown when calling stack build is

Could not parse 'stack.yaml':
Aeson exception:
Error in $.packages[1]: failed to parse field 'packages': parsing Text failed, expected String, but encountered Object
See http://docs.haskellstack.org/en/stable/yaml_configuration/