Matplotlib version fix

[kujaku11]

With matplotlib 3.5, there are some changes to the keywords that cause errors in the plotting schemes.

Description

I changed the required matplotlib package to be <=3.4 to keep the plotting tools working for now until we make all the changes.

Motivation and Context

Addresses issue #166 and probably a few other plotting errors.

How Has This Been Tested?

Screenshots (if appropriate):

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.