Architecture read from node-gyp incorrectly

[dbkr]

https://github.com/neon-bindings/neon/blob/master/crates/neon-sys/build.rs#L96 reads the architecture from node-gyp configure, but the value printed is just the architecture that node is running on, not the target architecture (https://github.com/nodejs/node-gyp/blob/3555ff4f0031f067bda9a49cbb2dbe6c04f4b5c7/bin/node-gyp.js#L45).

This means that building on an architecture other than that of the host machine's node binary will fail because the final link will use the node library path for the wrong architecture.