End .nojekyll file with newline

[dtolnay]

See https://stackoverflow.com/questions/729692/why-should-text-files-end-with-a-newline.

Before:

/path/to$  cat book/.nojekyll
This file makes sure that Github Pages doesn't process mdBook's output./path/to$  ▎

After:

/path/to$  cat book/.nojekyll
This file makes sure that Github Pages doesn't process mdBook's output.
/path/to$  ▎

[ehuss]

Thanks!