Trailing whitespace should be trimmed for neatness

[PPKFS]

Consider this: https://haskell.github.io/error-messages/messages/GHC-99623/example1/index.html

because the before has an extra trailing newline, the alignment is thrown off. This should probably be formatted the same way

[david-christiansen]

Good idea! Perhaps this can be automated as part of CI too.