openbsd: try pkg_add

Author: Mizux

ci/vagrant/openbsd/Vagrantfile

@@ -79,8 +79,8 @@ Vagrant.configure("2") do |config|
   # note: clang installed by default
   config.vm.provision "env", type: "shell", inline:<<-SHELL
   set -x
-  pkgin update
-  pkgin -y install git cmake
+  pkg_add -u
+  pkg_add git cmake
   SHELL
 
   config.vm.provision "file", source: "../../../CMakeLists.txt", destination: "$HOME/project/"