Fixed typo (vi leftover).

There was a trailing :w at a line, which didn't make sense in context
of the sentence/styling. Removed it, because I think it's a leftover
vi command.

CLA: trivial
Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7875)