Add a blank line after the commit message's first

[dwoffinden]

From the git man page: https://mirrors.edge.kernel.org/pub/software/scm/git/docs/git-commit.html#_discussion

Though not required, it’s a good idea to begin the commit message with a single short (less than 50 character) line summarizing the change, followed by a blank line and then a more thorough description. The text up to the first blank line in a commit message is treated as the commit title, and that title is used throughout Git.

In my case it means that tig includes the full JSON metadata on one line D: