Update node_http2.cc

According to the description above, this should be checking whether frame->hd.type is NGHTTP2_GOAWAY, and the value of NGHTTP2_GOAWAY is 0x07. However, it is written as 0x03 here, which I think  it is a typo.

Author: hgqxjj

src/node_http2.cc

@@ -1206,7 +1206,7 @@ int Http2Session::OnFrameNotSent(nghttp2_session* handle,
     // closed but the Http2Session will still be up causing a memory leak.
     // Therefore, if the GOAWAY frame couldn't be send due to
     // ERR_SESSION_CLOSING we should force close from our side.
-    if (frame->hd.type != 0x03) {
+    if (frame->hd.type != NGHTTP2_GOAWAY) {
       return 0;
     }
   }