title: Travis CI Fails to Build with a Code Signing Error
body: <p>Travis CI fails to build my app because the Xcode project is set up to require code signing and Travis doesn't have my certificates. I could fix this by disabling code signing, but then sandboxing and entitlements won't work. I know when building from the command line ordinarily, you can pass <code>CODE_SIGN_IDENTITY="" CODE_SIGNING_REQUIRED=NO</code> to <code>xcodebuild</code> to disable the code signing, but <em>how do you do this in Travis CI</em>?</p>
  
  <p>Here's my <code>.travis.yml</code>:</p>
  
  <pre><code>language: objective-c
  xcode_workspace: "Mac Linux USB Loader.xcworkspace"
  xcode_scheme: "Mac Linux USB Loader"
  </code></pre>
  
  <p>And here's the error (I've code out many previous lines referring to Cocoapods, as they're not relevant:</p>
  
  <pre><code>Check dependencies
  Code Sign error: No code signing identities found: No valid signing identities (i.e. certificate and private key pair) matching the team ID “T47PR9EQY5” were found.
  </code></pre>