Fix account.hashMessage with non-ASCII characters

[ryanio]

Description

This PR aims to fix #3523 where hashing a message with non-ASCII characters should work.

The first commit adds a failing test, and the second commit fixes the hashMessage method by handling conversion of utf8 data.

Type of change

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

Checklist:

• I have selected the correct base branch.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• Any dependent changes have been merged and published in downstream modules.
• I ran npm run dtslint with success and extended the tests and types if necessary.
• I ran npm run test:unit with success.
• I ran npm run test:cov and my test cases cover all the lines and branches of the added code.
• I ran npm run build-all and tested the resulting files from dist folder in a browser.
• I have updated the CHANGELOG.md file in the root folder.
• I have tested my code on the live network.

[coveralls]

Coverage increased (+0.003%) to 89.622% when pulling 077e416 on issue/3523 into 5a09ca0 on 1.x.

[cgewecke]

Sweet! Looks good 💯