Adding /healthz to NGINX Docker image

I am trying to deploy an nginx docker image. I need to create an endpoint to be used by my readiness probe, this should be a simple /healthz endpoint that returns a 200 / OK.

I have tried the below, however this causes the browser to download a file containing the response and not render it as doc.

server {
    listen       80;
    server_name  localhost;

    location /healthz {
        return 200 "OKn";
    }

    location / {

        root   /usr/share/nginx/html;
        index  index.html index.htm;
        try_files $uri /index.html;                 
    }

    # redirect server error pages
    #
    error_page   500 502 503 504  /50x.html;
    location = /50x.html {
        root   /usr/share/nginx/html;
    }

}

Source: StackOverflow