[Cashtab] Match seed phrase collapse title position

Summary: Related to task T2349. Text in seed phrase collapse should be centered in Configure.js

Test Plan:
cd web/casthab && npm start
navigate to configure page
observe that the text in the seed phrase collapse is now centered

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D11310