Try to fix travis

.travis.yml

@@ -38,7 +38,7 @@ matrix:
       env:
         - TOXENV=short
     - os: osx
-      osx_image: xcode9.2
+      osx_image: xcode9.3
       language: objective-c
       env:
         - TRAVIS_PYTHON_VERSION=3.6

util/travis_osx_install.sh

 #!/bin/bash
 brew update
 brew install ccache
-# brew outdated openssl || brew upgrade openssl
-# brew install openssl@1.1
+brew outdated openssl || brew upgrade openssl
+brew install openssl@1.1
 
 export CFLAGS="-I$(brew --prefix openssl)/include $CFLAGS"
 export LDFLAGS="-L$(brew --prefix openssl)/lib $LDFLAGS"