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 b5bdff8.

PR-URL: #8861
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ilkka Myller <ilkka.myller@nodefield.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

Makefile

@@ -162,7 +162,7 @@ test/addons/.buildstamp: config.gypi \
 	deps/npm/node_modules/node-gyp/package.json \
 	$(ADDONS_BINDING_GYPS) $(ADDONS_BINDING_SOURCES) \
 	deps/uv/include/*.h deps/v8/include/*.h \
-	src/node.h src/node_buffer.h src/node_object_wrap.h \
+	src/node.h src/node_buffer.h src/node_object_wrap.h src/node_version.h \
 	test/addons/.docbuildstamp
 	# Cannot use $(wildcard test/addons/*/) here, it's evaluated before
 	# embedded addons have been generated from the documentation.