title: Runner is undefined in query of Knex.js
body: <p>I tried to use Knex.js on Node.js by following code:</p>
  
  <pre><code>var Promise = require("bluebird");
  var knex = require("knex")({  
      client: 'pg',
      user     : 'username',
      database : 'database',
      password: "password",
      migrations: {
          tableName: 'knex_migrations'
      },
      pool: {
          min: 0,
          max: 7
      }
  });
  
  knex.select("*").from("users").then(function(rows){
      console.log(rows);
  });
  </code></pre>
  
  <p>But, it threw an error about <code>Runner</code> object as follows:</p>
  
  <pre><code>/path/to/myapp/node_modules/knex/lib/interface.js:27
      return new Runner(this).run().then(onFulfilled, onRejected);
             ^
  TypeError: undefined is not a function
      at QueryBuilder_PG.Target.then (/path/to/myapp/node_modules/knex/lib/interface.js:27:12)
      at Object.&lt;anonymous&gt; (/path/to/myapp/test.js:14:32)
      at Module._compile (module.js:456:26)
      at Object.Module._extensions..js (module.js:474:10)
      at Module.load (module.js:356:32)
      at Function.Module._load (module.js:312:12)
      at Function.Module.runMain (module.js:497:10)
      at startup (node.js:119:16)
      at node.js:906:3
  </code></pre>
  
  <p>When I try to use <code>stream</code>, <code>pipe</code>, <code>exec</code> and <code>transaction</code>, same error occurred.<br>
  Please tell me how to solve this problem...</p>