title: MTLCreateSystemDefaultDevice() returning nil on iPad with iOS 10.3
body: <p>I am trying to do some fluid simulation with Google's Liquidfun and Metal, using an iPad running iOS 10.3. However, the initial call to MTLCreateSystemDefaultDevice() is returning nil. </p>
  
  <p>I have the following console log, so I know that Metal is supported on the iPad, but I am not sure how to debug this issue. </p>
  
  <pre><code>2018-07-02 20:28:44.547645-0500 chem-lab-practical[529:464344] [DYMTLInitPlatform].
  platform initialization successful 2018-07-02 20:28:44.781763-0500 
  chem-lab-practical[529:464294] Metal GPU Frame Capture Enabled 2018-07-02 
  20:28:44.783609-0500 chem-lab-practical[529:464294] Metal API Validation Enabled 
  (lldb)
  </code></pre>
  
  <p>I have not found similar questions on stack overflow and am a beginner to using Metal, so I am not sure how to begin to debug this issue.</p>