Use govspeak version with fix for address markdown

www.agileplannerapp.com/boards/173808/cards/5680

the address markdown ($A) required an extra blank
line preceding it for preview toggle to function.
this was confusing for the editors.

this change fixed the issue:
https://github.com/alphagov/govspeak/pull/43
Merge pull request #1687 from alphagov/use-govspeak-with-address-markdown-fix

Use govspeak version with fix for address markdown