fix(build): use node-gyp@9.3.1

Since nodejs/node-gyp@02480f6, this is
incompatible with Node.js 12.x since newer 'make fetch happen' specifies
a 14.x+ requirement, which *still* breaks node-ffi-napi.

As of nodejs/node-gyp@33391db, the deps
got updated so that the 'latest' version won't install anymore.

"is vulnerable", how does this *matter* for a client application? aaaaaa
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
aaaaaaaaaaaaaaaaa...

ext/native-doc-gen/build.sh

@@ -21,7 +21,7 @@ YARN="$NODE $ROOT/yarn_cli.js"
 # install yarn deps
 cd $ROOT/../native-doc-tooling/
 
-$YARN global add node-gyp
+$YARN global add node-gyp@9.3.1
 $YARN
 
 cd $ROOT/../natives/