Tephrabase: Set encoding to utf-8

[christopher-angel]

Description

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

This changes the text encoding for tephrabase from ISO-8859-1 to UTF-8

Types of changes

• [ ] New dataset
• [ ] Fix: Typographical Errors
• [x] Encoding adjustments
• [ ] New Field(s) added to each data object
• [ ] Remove Field(s) from each data object
• [ ] Other

Checklist:

• [x] Data is encoded to UTF-8
• [x] Data follows GeoJSON standards
• [ ] I have performed a self-review of my own dataset
• [ ] I understand I still need to "Process" my data in the main DataARC Contributor Tool