[Cashtab] Nav menu fix post label rebrand

Summary:
Linked to T1926
Changing "Token" to "eToken" in nav menu squashed nav bar in Firefox. This patch adjusts the font size to mitigate the cosmetic issue.

Test Plan:

• npm start
• manually adjust browser width and verify menu maintains its shape in both firefox and browser
• npm run extension
• ensure menu maintains shape in browser extension mode

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D10382