Fixing undefined currency value for contribution notification

[ryanml]

Fixes: #14417

Basically the transaction keys were swapped, trying to access the currency prop first as opposed to fiat. Contribution map is structured like so:

{ "fiat": Map { "amount": 10, "currency": "BAT" }, "rates": Map { "EUR": 0.16415440004057, "USD": 0.19355117, "BCH": 0.00022834810733109726, "BTC": 0.0000327, "DASH": 0.0007821603506058262, "BTG": 0.005958015042318794, "XRP": 0.36440067259188086, "ETH": 0.0004051167013833253, "LTC": 0.0020486297689414294 }, "satoshis": undefined, "altcurrency": "BAT", "probi": "10000000000000000000", "fee": undefined }

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.
• Request a security/privacy review as needed. (Ask a Brave employee to help if you cannot access this document.)

Test Plan:

Defined in #14417

Reviewer Checklist:

• Request a security/privacy review as needed if one was not already requested.

Tests

• Adequate test coverage exists to prevent regressions
• Tests should be independent and work correctly when run individually or as a suite ref
• New files have MPL2 license header

[jasonrsadler]

++ 🥇

[bsclifton]

don't forget to merge this into 0.23.x 😄

[jasonrsadler]

Doing that now!!!!!!!!!! 😄

[jasonrsadler]

master: 081069c
0.23.x: 90f3180