src: update NODE_MODULE_VERSION to 55

Major V8 updates are usually API/ABI incompatible with previous
versions. This commit adapts NODE_MODULE_VERSION for V8 5.8.

Refs: https://github.com/nodejs/CTC/blob/master/meetings/2016-09-28.md
PR-URL: nodejs#12784
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>

src/node_version.h

@@ -73,6 +73,6 @@
  * an API is broken in the C++ side, including in v8 or
  * other dependencies.
  */
-#define NODE_MODULE_VERSION 54 /* Node.js v8.0.0 */
+#define NODE_MODULE_VERSION 55 /* Node.js v8.0.0 */
 
 #endif  // SRC_NODE_VERSION_H_