use org.json instead of Gson

src/main/java/com/github/nkzawa/engineio/client/HandshakeData.java

@@ -0,0 +1,27 @@
+package com.github.nkzawa.engineio.client;
+
+
+import org.json.JSONArray;
+import org.json.JSONObject;
+
+public class HandshakeData {
+
+    public String sid;
+    public String[] upgrades;
+    public long pingInterval;
+    public long pingTimeout;
+
+    /*package*/ HandshakeData(JSONObject data) {
+        JSONArray upgrades = data.getJSONArray("upgrades");
+        int length = upgrades.length();
+        String[] _upgrades = new String[length];
+        for (int i = 0; i < length; i ++) {
+            _upgrades[i] = upgrades.getString(i);
+        }
+
+        this.sid = data.getString("sid");
+        this.upgrades = _upgrades;
+        this.pingInterval = data.getLong("pingInterval");
+        this.pingTimeout = data.getLong("pingTimeout");
+    }
+}