build: make addons build dep. on node_version.h

Make the `test/addons/.buildstamp` file dependent on
`src/node_version.h` since addons need to be re-compiled after
`NODE_MODULE_VERSION` bumps, e.g. as it happened recently
in b5bdff87.

PR-URL: https://github.com/nodejs/node/pull/8861


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ilkka Myller <ilkka.myller@nodefield.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>