cmd: fmt the main.go, add cmd.go for placeholder.

cmd/cmd.go

@@ -0,0 +1,19 @@
+// Copyright (C) 2017 go-nebulas authors
+//
+// This file is part of the go-nebulas library.
+//
+// the go-nebulas library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// the go-nebulas library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with the go-nebulas library.  If not, see <http://www.gnu.org/licenses/>.
+//
+
+package cmd

cmd/neb/main.go

@@ -25,8 +25,8 @@ import (
 	"syscall"
 	"time"
 
-	"github.com/nebulasio/go-nebulas/core"
 	"github.com/nebulasio/go-nebulas/consensus/pow"
+	"github.com/nebulasio/go-nebulas/core"
 	"github.com/nebulasio/go-nebulas/net"
 	"github.com/nebulasio/go-nebulas/net/messages"