Warn on line breaks between subject and body about commitplease

[scottgonzalez]

I think what you're really asking for is all commits to have a trailing new line.

[jzaefferer]

I think Dave just didn't have commitplease installed (because it wouldn't install), otherwise it would have rejected the commit message. I just copied the message from jquery's git log and tried to use it, commitplease rejected it:

Invalid commit message, please fix the following issues:

- Second line must always be empty

Commit message was:

Build: Add "browser" keyword for npm
(cherry picked from commit 108428bcabb7027852ecd656b98f110a444039d0)
# Please enter the commit message for your changes. Lines starting
# with '#' will be ignored, and an empty message aborts the commit.
# On branch replace-symlink-with-copy
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#
#   new file:   foo
#   modified:   test.js
#