travis: build darwinssl on macos 10.12

... as building on 10.13.x before 10.13.4 leads to link errors.

Assisted-by: Nick Zitzmann
Fixes #2835
Closes #2845

diff --git a/.travis.yml b/.travis.yml
index e713fcef707f9bec4ed3837c1c9b2d0ad5a5a7ae..68423b8afd767aff5aa4829692ff1cc52355cff4 100644 (file)
--- a/.travis.yml
+++ b/.travis.yml
@@ -101,6 +101,7 @@ matrix:
           env: T=debug C="--with-ssl=/usr/local/opt/libressl --with-libmetalink"
         - os: osx
           compiler: clang
+          osx_image: xcode9.2
           env: T=debug C="--without-ssl --with-darwinssl --with-libmetalink"
         - os: osx
           compiler: clang