Load version from package.json. closes #2

Author: jimmycuadra

lib/cli.js

@@ -1,6 +1,7 @@
 {Command} = require "commander"
 Bang      = require "./bang"
 {exec}  = require "child_process"
+package = require "../package.json"
 
 # Command line interface to [Bang](https://github.com/jimmycuadra/bang).
 module.exports = class CLI
@@ -12,7 +13,7 @@ module.exports = class CLI
     @bang     = mockBang or new Bang
     @program  = new Command
 
-    @program.version("0.2.1")
+    @program.version(package.version)
       .usage("[options] [key] [value]")
       .option("-d, --delete", "delete the specified key")
       .option("-h, --help", "get help")