Use utf-8 encoding to read generated .tex files.

[OliverStrait]

Overview: What does this pull request change?

Fixes a little decoding error when handling tex-errors.

Motivation and Explanation: Why and how do your changes improve the library?

• Python uses default encoding provided by OS.
• In windows, system default text encoding is some reason a ancient Microsoft cp1252-encoding, a version of ANSI.
• Tex will produce Utf-8 encoded files and current system will produce decoding error if tex file include any utf-8 characters.

Reviewer Checklist

• The PR title is descriptive enough for the changelog, and the PR is labeled correctly
• If applicable: newly added non-private functions and classes have a docstring including a short summary and a PARAMETERS section
• If applicable: newly added functions and classes are tested

[JasonGrace2282]

This seems fine, if tests pass let's merge this. Thanks!