[Cashtab] Move dependency key next to devDependencies

Summary: It's nice to have them all next to each other

Test Plan:
Confirm diff is only moving a json object, no code changes

npm test && npm run build

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D15246