src: update NODE_MODULE_VERSION to 61

Major V8 updates are usually API/ABI incompatible with previous
versions. This commit adapts NODE_MODULE_VERSION for V8 6.4.

Refs: https://github.com/nodejs/CTC/blob/master/meetings/2016-09-28.md

PR-URL: #17489
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>
Reviewed-By: Ali Ijaz Sheikh <ofrobots@google.com>

src/node_version.h

@@ -104,10 +104,11 @@
  * V8 6.1: 58
  * V8 6.2: 59
  * V8 6.3: 60
+ * V8 6.4: 61
  *
  * More information can be found at https://nodejs.org/en/download/releases/
  */
-#define NODE_MODULE_VERSION 60
+#define NODE_MODULE_VERSION 61
 
 // the NAPI_VERSION provided by this version of the runtime
 #define NAPI_VERSION  2