Disable SSL tests for macOS on Travis CI

because the specs require certs from .travis_ssl.sh installed in
/etc/mysql which is inaccessible without root on macOS.

A more involved fix would be to parameterize the paths in the specs and
adapt the .travis_ssl.sh script to work properly on macOS.

Author: felixbuenemann

.travis.yml

@@ -20,6 +20,7 @@ before_install:
     bash -c " # Install MySQL is OS=darwin
     if [[ x$OSTYPE =~ ^xdarwin ]]; then
       brew install mysql
+      echo ssl = 0 >> /usr/local/etc/my.cnf
       mysql.server start
     fi
     "