load and save method fixed in Wallet class

[nivida]

Description

Fixes #2647

Type of change

• Bug fix

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 warnings.
• I have updated or added types for all modules I've changed
• Any dependent changes have been merged and published in downstream modules.
• I ran npm run test in the root folder with success and extended the tests if necessary.
• I ran npm run build in the root folder and tested it in the browser and with node.
• I ran npm run dtslint in the root folder and tested that all my types are correct
• I have tested my code on an ethereum test network.

[coveralls]

Coverage remained the same at 95.374% when pulling 8a99c01 on issue/2647 into c5372b6 on 1.0.

[coveralls]

Coverage remained the same at 95.374% when pulling 8a99c01 on issue/2647 into c5372b6 on 1.0.