Update json_dict_to_dataframe delimiter to ":" rather than "-" to avo…

[edwardxtg]

…id issues

Description

Please explain the changes you made here.

Checklist

• Dependencies install correctly in a clean environment and code executes;
• Test coverage extended; created tests fail without the change (if possible);
• All tests passing;
• Commits follow a type convention (e.g. https://gist.github.com/brianclements/841ea7bffdb01346392c#type);
• Extended the README, documentation and/or docstrings, if necessary;