src: fix ssize_t error from nghttp2.h

The "node_http2.h" include reordering enforced by clang-format broke
Electron's Node.js upgrade on Windows. ssize_t is a part of the POSIX
standard and it's not available on Windows, so the fix for this is to
include "node.h" which typedefs it on Windows in
https://github.com/nodejs/node/blob/bb4dff783ddb3b20c67041f7ccef796c335c2407/src/node.h#L212-L220.

Refs: electron/electron#35350 (comment)
Signed-off-by: Darshan Sen <raisinten@gmail.com>

src/node_http2.h

@@ -5,6 +5,9 @@
 
 // FIXME(joyeecheung): nghttp2.h needs stdint.h to compile on Windows
 #include <cstdint>
+// clang-format off
+#include "node.h"  // nghttp2.h needs ssize_t
+// clang-format on
 #include "nghttp2/nghttp2.h"
 
 #include "env.h"