Unify readme code examples with 'const'

* It is better to be unified.
* Recently, 'const' is often used.

Readme.md

@@ -261,7 +261,7 @@ You use `.arguments` to specify the arguments for the top-level command, and for
 
 
 ```js
-var program = require('commander');
+const program = require('commander');
 
 program
   .version('0.1.0')
@@ -285,7 +285,7 @@ console.log('environment:', envValue || "no environment given");
  append `...` to the argument name. For example:
 
 ```js
-var program = require('commander');
+const program = require('commander');
 
 program
   .version('0.1.0')
@@ -311,7 +311,7 @@ The action handler gets passed a parameter for each argument you declared, and o
 command object itself. This command argument has the values for the command-specific options added as properties.
 
 ```js
-var program = require('commander');
+const program = require('commander');
 
 program
   .command('rm <dir>')
@@ -337,7 +337,7 @@ You handle the options for an executable (sub)command in the executable, and don
 
 ```js
 // file: ./examples/pm
-var program = require('commander');
+const program = require('commander');
 
 program
   .version('0.1.0')
@@ -389,7 +389,7 @@ Options:
  * Module dependencies.
  */
 
-var program = require('commander');
+const program = require('commander');
 
 program
   .version('0.1.0')
@@ -437,8 +437,8 @@ Optional callback cb allows post-processing of help text before it is displayed.
 If you want to display help by default (e.g. if no command was provided), you can use something like:
 
 ```js
-var program = require('commander');
-var colors = require('colors');
+const program = require('commander');
+const colors = require('colors');
 
 program
   .version('0.1.0')
@@ -515,7 +515,7 @@ the inspector port is incremented by 1 for the spawned subcommand.
 ## Examples
 
 ```js
-var program = require('commander');
+const program = require('commander');
 
 program
   .version('0.1.0')
@@ -528,7 +528,7 @@ program
   .description('run setup commands for all envs')
   .option("-s, --setup_mode [mode]", "Which setup mode to use")
   .action(function(env, options){
-    var mode = options.setup_mode || "normal";
+    const mode = options.setup_mode || "normal";
     env = env || 'all';
     console.log('setup for %s env(s) with %s mode', env, mode);
   });

Readme_zh-CN.md

@@ -256,7 +256,7 @@ program
 你可以通过使用 `.arguments` 来为最顶级命令指定参数，对于子命令来说参数都包括在 `.command` 调用之中了。尖括号(e.g. `<required>`)意味着必须的输入，而方括号(e.g. `[optional]`)则是代表了可选的输入
 
 ```js
-var program = require('commander');
+const program = require('commander');
 
 program
   .version('0.1.0')
@@ -279,7 +279,7 @@ console.log('environment:', envValue || "no environment given");
 一个命令有且仅有最后一个参数是可变的，你需要在参数名后加上 `...` 来使它可变，例如
 
 ```js
-var program = require('commander');
+const program = require('commander');
 
 program
   .version('0.1.0')
@@ -304,7 +304,7 @@ program.parse(process.argv);
 操作处理程序会接收每一个你声明的参数的变量，和一个额外的参数——这个命令对象自己。这个命令的参数包括添加的命令特定选项的值。
 
 ```js
-var program = require('commander');
+const program = require('commander');
 
 program
   .command('rm <dir>')
@@ -331,7 +331,7 @@ Commander 将会尝试在入口脚本（例如 `./examples/pm`）的目录中搜
 
 ```js
 // file: ./examples/pm
-var program = require('commander');
+const program = require('commander');
 
 program
   .version('0.1.0')
@@ -380,7 +380,7 @@ Options:
  * Module dependencies.
  */
 
-var program = require('commander');
+const program = require('commander');
 
 program
   .version('0.0.1')
@@ -427,8 +427,8 @@ Examples:
 如果你想显示默认的帮助（例如，如果没有提供命令），你可以使用类似的东西：
 
 ```js
-var program = require('commander');
-var colors = require('colors');
+const program = require('commander');
+const colors = require('colors');
 
 program
   .version('0.1.0')
@@ -504,7 +504,7 @@ node -r ts-node/register pm.ts
  ## 例子
 
 ```js
-var program = require('commander');
+const program = require('commander');
 
 program
   .version('0.1.0')
@@ -517,7 +517,7 @@ program
   .description('run setup commands for all envs')
   .option("-s, --setup_mode [mode]", "Which setup mode to use")
   .action(function(env, options){
-    var mode = options.setup_mode || "normal";
+    const mode = options.setup_mode || "normal";
     env = env || 'all';
     console.log('setup for %s env(s) with %s mode', env, mode);
   });