ensure JSON.parse gets a string, not an HTTParty::Response object

[rhec]

Description

There was already some normalization of response.body to a string, so I pulled that out above the parsing so it could be re-used.

Related Issue

Fixes #65

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.