start-jupyter: create ~/.ssh if it doesn't exist already

start-jupyter

@@ -340,6 +340,7 @@ function main () {
 
     echo "Establishing ssh master connection."
     # Set up control master for connection sharing
+    mkdir -p "${HOME}/.ssh"
     ssh_socket_dir="$(mktemp -d "${HOME}/.ssh/socket.XXXXX")"
     ssh_frontend "" "-MNf"