fix nodejs/node-gyp tarball version

node-gyp needs to know about the installed Node.js version.

This needs to be updated each time Node.js is upgraded. May we do this
automatically with sed in Makefile pre-patch section ?

Index: patches/patch-deps_npm_node_modules_node-gyp_lib_install_js
===================================================================
RCS file: /cvs/ports/lang/node/patches/patch-deps_npm_node_modules_node-gyp_lib_install_js,v
retrieving revision 1.11
diff -u -p -r1.11 patch-deps_npm_node_modules_node-gyp_lib_install_js
--- patches/patch-deps_npm_node_modules_node-gyp_lib_install_js 24 Nov 2019 18:42:28 -0000 1.11
+++ patches/patch-deps_npm_node_modules_node-gyp_lib_install_js 2 Apr 2020 07:18:39 -0000
@@ -11,7 +11,7 @@ Index: deps/npm/node_modules/node-gyp/li

// now download the node tarball
- var tarPath = gyp.opts.tarball
-+ var tarPath = gyp.opts['tarball'] || '/usr/local/share/node/node-v12.9.0.tar.gz' // Fix for OpenBSD
++ var tarPath = gyp.opts['tarball'] || '/usr/local/share/node/node-v12.13.1.tar.gz' // Fix for OpenBSD
var badDownload = false
var extractCount = 0
var contentShasums = {}