Node.js: response body chunk can now be a Uint8Array.

Starting from Node.js 15.0.0 the chunk parameter of the response.write()
can be a Uint8Array.

This closes #870 issue on GitHub.

src/nodejs/unit-http/http_server.js

@@ -243,8 +243,11 @@ ServerResponse.prototype._writeBody = function(chunk, encoding, callback) {
     }
 
     if (chunk) {
-        if (typeof chunk !== 'string' && !(chunk instanceof Buffer)) {
-            throw new TypeError('First argument must be a string or Buffer');
+        if (typeof chunk !== 'string' && !(chunk instanceof Buffer ||
+                chunk instanceof Uint8Array)) {
+            throw new TypeError(
+                'First argument must be a string, Buffer, ' +
+                'or Uint8Array');
         }
 
         if (typeof chunk === 'string') {