Always save the buffer, even if it is unmodified

There are some unexpected side effects when the buffer isn't saved because it is unmodified. 

- People expect whitespace to be removed when they press `cmd-s`. But if the buffer wasn't changed it won't be because the whitespace package listens for the `will-be-saved` event.

- People use `cmd-s` to update the file's modified date. They rely on this functionality to trigger scripts.

Also, there doesn't seem to be much downside to always saving.