🐛 Fix EADDRINUSE errors on Linux/Mac

Clean up last socket on Linux-based systems to avoid EADDRINUSE errors
poping up.

App.js

@@ -8,6 +8,9 @@ var ipc = require('ipc');
 var net = require('net');
 var util = require('util');
 var events = require('events');
+var path = require('path');
+var os = require('os');
+var fs = require('fs');
 
 /**
  * App
@@ -32,7 +35,10 @@ function App() {
 
 util.inherits(App, events.EventEmitter);
 module.exports = App;
-App.socket = '\\\\.\\pipe\\piano-sock';
+
+// create pipe on Windows and socks on Linux-based environments
+App.socket = (process.platform === 'win32') ?
+    '\\\\.\\pipe\\piano-sock' : path.join(os.tmpdir(), 'piano.sock');
 
 /**
  * Add a new window
@@ -129,6 +135,18 @@ App.prototype.chainOptions = function (callback) {
 App.prototype.startServer = function () {
     var server;
     
+    if (process.platform !== 'win32') {
+        // try to unlink older socket if it exists, if it doesn't,
+        // ignore ENOENT errors
+        try {
+            fs.unlinkSync(App.socket);
+        } catch (e) {
+            if (e.code !== 'ENOENT') {
+                throw e;
+            }
+        }
+    }
+    
     server = net.createServer(function (connection) {
         connection.on('data', function (data) {
             this.windows[0].focus();