exclude NODE_EMBEDDER_MODULE_VERSION string (#23)

When extracting the module version from `src/node_version.h`, ignore
the line:
#define NODE_MODULE_VERSION NODE_EMBEDDER_MODULE_VERSION

This will pick up the default value from the header as the official
Node.js builds do not define `NODE_EMBEDDER_MODULE_VERSION`.

Fixes: #20
Refs: nodejs/node#49279

dist-indexer.js

@@ -325,7 +325,7 @@ function fetchModVersion (gitref, callback) {
       return callback(err)
     }
 
-    let m = rawData.match(/^#define NODE_MODULE_VERSION\s+([^\s]+)\s+.+$/m)
+    let m = rawData.match(/^#define NODE_MODULE_VERSION\s+((?!NODE_EMBEDDER_MODULE_VERSION)[^\s]+)\s+.+$/m)
     version = m && m[1]
 
     if (version) {