Updates to Mintable ERC20

[rymcol]

Description

• Updates decimals -> 6
• clarifies naming

Motivation and Context

The underlying asset we are representing in testing is also six decimals, so this change will make testing easier

How Has This Been Tested?

manual

Types of changes (remove all unchecked types)

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• If my change requires a change to the documentation, I have updated the documentation accordingly, and in either case, have checked this box to attest to my assessment of this requirement with regard to my change.
• If my change requires additions or updates to any deployment scripts to ensure that the protocol is functional (Makefile, Dockerfile, Forge Script, etc.), I have made these changes, and in either case, have checked this box to attest to my assessment of this requirement with regard to my change.
• [xs] If my change requires additional test coverage, I have created those tests accordingly, and in either case, have checked this box to attest to my assessment of this requirement with regard to my change.

[evchip]

ty!