title: arrary.includes ok in vscode but not tsc / tsify
body: <p>using typescript I am trying to call array.includes. I have tsconfig set to say target = es6. In vscode there are no complaints, all works fine (It moaned big time till I changed target from es5 to es6)</p>
  
  <p>But running through command line tsc (or tsify) it complains that <code>includes</code> is not valid </p>
  
  <pre><code>FuncLib.ts(15,23): error TS2339: Property 'includes' does not exist on type 'string[]'.
  </code></pre>
  
  <p>npm says I have typescript 2.9.1. Do I have to explicitly tell tsc (or tsifY) to read my tsconfig file?</p>