Changed SessionID format.

Pusher libs are validating the sessionID format. So I need to conform
with its format.

utils/utils_test.go

@@ -0,0 +1,20 @@
+// Copyright 2015 Claudemiro Alves Feitosa Neto. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package utils
+
+import (
+	"fmt"
+	"regexp"
+	"testing"
+)
+
+func TestGenerateSession(t *testing.T) {
+	sessionID := GenerateSessionID()
+
+	fmt.Println(sessionID)
+	if matched, _ := regexp.MatchString("^\\d+\\.\\d+$", sessionID); !matched {
+		t.Errorf("Must match ^\\d+\\.\\d+$, value: '%s'", sessionID)
+	}
+}