Drop support for LibreSSL < 2.3topic/docker-image-update

We have changed the support policy for LibreSSL: we now support only
maintained stable branches.

Quoting from libressl.org[1]:

> LibreSSL transitions to a new stable release branch every 6 months in
> coordination with the OpenBSD development schedule. LibreSSL stable
> branches are updated for 1 year after their corresponding OpenBSD
> branch is tagged for release.

So, LibreSSL 2.2, which was shipped by OpenBSD 5.8 released on 2015-08,
is no longer supported officially by the OpenBSD team.

[1] http://www.libressl.org/releases.html

1 files changed, 1 insertions, 1 deletions

diff --git a/History.md b/History.md
index bd392dac..029426fb 100644
--- a/History.md
+++ b/History.md
@@ -17,7 +17,7 @@ Supported platforms
 
 * OpenSSL 1.0.0, 1.0.1, 1.0.2, 1.1.0
 * OpenSSL < 0.9.8 is no longer supported.
-* LibreSSL 2.1, 2.2, 2.3, 2.4
+* LibreSSL 2.3, 2.4, 2.5
 * Ruby 2.3, 2.4
 
 Notable changes