Merge pull request #12 from jorisbontje/go_no_block_difficulty

fix for go rpc not exposing block difficulty

models/node.js

@@ -49,7 +49,7 @@ Node.prototype.update = function()
 
 	if(this.info.stats.peers != null) {
 		this.info.stats.block = eth.block(parseInt(eth.number));
-		if(this.info.stats.block.hash != '?'){
+		if(this.info.stats.block.hash != '?' && typeof this.info.stats.block.difficulty !== 'undefined'){
 			this.info.stats.block.difficulty = this.web3.toDecimal(this.info.stats.block.difficulty);
 		}
 		this.info.stats.mining = eth.mining;
@@ -65,4 +65,4 @@ Node.prototype.update = function()
 	return this.info;
 };
 
-module.exports = Node;
+module.exports = Node;