Fix content-type suggestion in inline documentation

The inline docs were displaying "content-type": "json", which isn't valid. Updated across functions to use "application/json":

/**
 * Make a POST request
 * @public
 * @example
 *  post("/myendpoint", {
 *      body: {"foo": "bar"},
 *      headers: {"content-type": "application/json"},
 *      authentication: {username: "user", password: "pass"},
 *    },
 *    function(state) {
 *      return state;
 *    }
 *  )
 * @function
 * @param {string} path - Path to resource
 * @param {object} params - Body, Query, Headers and Authentication parameters
 * @param {function} callback - (Optional) Callback function
 * @returns {Operation}
 */