Update GraphDatabase._coffee

This could be usefull when you are tired and you waste an entire hour trying to understand why this (see missing `.join('\n');` after query)
```
var query = [ "CREATE (n:Group {name:'pippo'}) return n"];
db.query(query, undefined, function(ee, res){
	if(ee){
		console.log(ee);
		throw ee;
	}
	console.log(res.id);
});
```

gives you this really usefull error
```
{ [Error: Unknown Neo4j error (status 500).] message: 'Unknown Neo4j error (status 500).' }
```