build: use macOS 10.14 SDK

Co-Authored-By: Carl Dong <accounts@carldong.me>

ci/test/00_setup_env_mac.sh

@@ -8,7 +8,7 @@ export LC_ALL=C.UTF-8
 
 export HOST=x86_64-apple-darwin16
 export PACKAGES="cmake imagemagick libcap-dev librsvg2-bin libz-dev libbz2-dev libtiff-tools python3-dev python3-setuptools"
-export OSX_SDK=10.11
+export OSX_SDK=10.14
 export RUN_UNIT_TESTS=false
 export RUN_FUNCTIONAL_TESTS=false
 export GOAL="deploy"