[e.cash] add style rule for blog code blocks

Summary: Fixing issue of text not breaking on code blocks as seen here /blog/ecash-node-daemon-setup-guide

Test Plan: preview the site and check out /blog/ecash-node-daemon-setup-guide. Code blocks should have the text wrap

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Subscribers: bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D15320