Method append

out/cli.cjs:6530–6541

* Append a value onto existing header * * @param String name Header name * @param String value Header value * @return Void

(name, value)

       * @return  Void
       */
      append(name, value) {
        name = `${name}`;
        value = `${value}`;
        validateName(name);
        validateValue(value);
        const key = find(this[MAP], name);
        if (key !== void 0) {
          this[MAP][key].push(value);
        } else {
          this[MAP][name] = [value];
        }
      }
      /**
       * Check for header name existence
       *