[PATCH] docs: Correct pre-release regex

[Stephen Finucane]

On Fri, 2017-05-26 at 09:29 +0100, Stephen Finucane wrote:
> There's no dot before the rc version.
> 
> Signed-off-by: Stephen Finucane <stephen at that.guru>
> Fixes: b02c43d ("docs: Add pre-release regex")

I'm going to go right ahead and merge this as a noddy fix that I've
validated locally.

Stephen