Fix compile errors appearing twice.

The `errorDetails` option for `stats.toJson` defaults to true.
This causes error messages to contain the same message twice.

Fixes webpack/webpack#3008

Author: SpaceK33z

lib/Server.js

@@ -11,6 +11,8 @@ var httpProxyMiddleware = require("http-proxy-middleware");
 var serveIndex = require("serve-index");
 var historyApiFallback = require("connect-history-api-fallback");
 
+var clientStats = { errorDetails: false };
+
 function Server(compiler, options) {
 	// Default options
 	if(!options) options = {};
@@ -32,7 +34,7 @@ function Server(compiler, options) {
 	compiler.plugin("compile", invalidPlugin);
 	compiler.plugin("invalid", invalidPlugin);
 	compiler.plugin("done", function(stats) {
-		this._sendStats(this.sockets, stats.toJson());
+		this._sendStats(this.sockets, stats.toJson(clientStats));
 		this._stats = stats;
 	}.bind(this));
 
@@ -389,7 +391,7 @@ Server.prototype.listen = function() {
 		if(this.hot) this.sockWrite([conn], "hot");
 
 		if(!this._stats) return;
-		this._sendStats([conn], this._stats.toJson(), true);
+		this._sendStats([conn], this._stats.toJson(clientStats), true);
 	}.bind(this));
 
 	sockServer.installHandlers(this.listeningApp, {