title: Setting process.env variables with grunt-env results in undefined
body: <p>I have this <code>grunt-env</code> task:</p>
  
  <pre><code>env: {
      dev: {
          NODE_ENV: 'dev',
          DEST: '&lt;%= config.dev %&gt;'
      },
      dist: {
          NODE_ENV: 'dist',
          DEST: '&lt;%= config.dist %&gt;'
      }
  },
  </code></pre>
  
  <p>Along with a simply task to test that <code>process.env.DEST</code> is getting set correctly.</p>
  
  <pre><code>grunt.registerTask('testEnv', function(){
    console.log(process.env.DEST);
  });
  </code></pre>
  
  <p>When I run it I get the expected output of <code>dev</code>.</p>
  
  <pre><code>Running "env:dev" (env) task
  
  Running "testEnv" task
  dev
  
  Done, without errors.
  </code></pre>
  
  <p>Now if I use <code>process.env.DEST</code> inside another grunt task I get the value as <code>undefined</code>.</p>
  
  <pre><code>Running tasks: env:dev, testEnv, concat:preload
  
  Running "env:dev" (env) task
  Verifying property env.dev exists in config...OK
  File: [no files]
  Options: (none)
  
  Running "testEnv" task
  dev
  
  Running "concat:preload" (concat) task
  Verifying property concat.preload exists in config...OK
  Files: app/scripts/preload/modernizr.js -&gt; undefined/scripts/preload.js
  Options: separator="\n", banner="", footer="", stripBanners=false, process=false, sourceMap=false, sourceMapName=undefined, sourceMapStyle="embed"
  Reading app/scripts/preload/modernizr.js...OK
  Writing undefined/scripts/preload.js...OK
  File undefined/scripts/preload.js created.
  
  Done, without errors.
  </code></pre>
  
  <p>You can see the undefined in this line <code>Files: app/scripts/preload/modernizr.js -&gt; undefined/scripts/preload.js</code>. It's a simple concat task where I want the output to be different dependent on the environment I set.</p>
  
  <pre><code>concat: {
      baseDir: '&lt;%= config.app %&gt;/scripts',
      preload: {
          src: ['&lt;%= concat.baseDir %&gt;/preload/*.js'],
          dest: process.env.DEST + '/scripts/preload.js'
      },
      libs: {
          src: ['&lt;%= concat.baseDir %&gt;/libs/*.js'],
          dest: process.env.DEST + '/scripts/vendors.js'
      }
  },
  </code></pre>
  
  <p>I've been at this for a day now and have no clue what I'm doing wrong. Any help would be greatly appreciated.</p>