title: Flutter fails on `flutter` command
body: <p>I'm following the <a href="http://flutter.io/getting-started/" rel="noreferrer">Getting Started with Flutter</a> guide and getting stuck when running the actual <code>flutter</code> command:</p>
  
  <pre><code>flutter init -o my_app
  Resolving dependencies...
  Error on line 17, column 16 of pubspec.yaml: Invalid version constraint: Could not parse version "^1.4.0". Unknown text at "^1.4.0".
    stack_trace: ^1.4.0
                 ^^^^^^
  Unhandled exception:
  Uncaught Error: FileSystemException: Cannot open file, path = '/Users/craig/Code/flutter/packages/flutter_tools/packages/sky_tools/executable.dart' (OS Error: No such file or directory, errno = 2)
  Stack Trace:
  #0      _File.open.&lt;anonymous closure&gt; (dart:io/file_impl.dart:349)
  #1      _RootZone.runUnary (dart:async/zone.dart:1151)
  #2      _Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:496)
  #3      _Future._propagateToListeners (dart:async/future_impl.dart:579)
  #4      _Future._completeWithValue (dart:async/future_impl.dart:339)
  #5      _Future._asyncComplete.&lt;anonymous closure&gt; (dart:async/future_impl.dart:401)
  #6      _asyncRunCallbackLoop (dart:async/schedule_microtask.dart:41)
  #7      _asyncRunCallback (dart:async/schedule_microtask.dart:48)
  #8      _runPendingImmediateCallback (dart:isolate-patch/isolate_patch.dart:84)
  #9      _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:131)
  
  #0      _rootHandleUncaughtError.&lt;anonymous closure&gt; (dart:async/zone.dart:883)
  #1      _asyncRunCallbackLoop (dart:async/schedule_microtask.dart:41)
  #2      _asyncRunCallback (dart:async/schedule_microtask.dart:48)
  #3      _runPendingImmediateCallback (dart:isolate-patch/isolate_patch.dart:84)
  #4      _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:131)
  Unhandled exception:
  Uncaught Error: FileSystemException: Cannot open file, path = '/Users/craig/Code/flutter/bin/cache/flutter_tools.snapshot' (OS Error: No such file or directory, errno = 2)
  Stack Trace:
  #0      _File.open.&lt;anonymous closure&gt; (dart:io/file_impl.dart:349)
  #1      _RootZone.runUnary (dart:async/zone.dart:1151)
  #2      _Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:496)
  #3      _Future._propagateToListeners (dart:async/future_impl.dart:579)
  #4      _Future._completeWithValue (dart:async/future_impl.dart:339)
  #5      _Future._asyncComplete.&lt;anonymous closure&gt; (dart:async/future_impl.dart:401)
  #6      _asyncRunCallbackLoop (dart:async/schedule_microtask.dart:41)
  #7      _asyncRunCallback (dart:async/schedule_microtask.dart:48)
  #8      _runPendingImmediateCallback (dart:isolate-patch/isolate_patch.dart:84)
  #9      _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:131)
  
  #0      _rootHandleUncaughtError.&lt;anonymous closure&gt; (dart:async/zone.dart:883)
  #1      _asyncRunCallbackLoop (dart:async/schedule_microtask.dart:41)
  #2      _asyncRunCallback (dart:async/schedule_microtask.dart:48)
  #3      _runPendingImmediateCallback (dart:isolate-patch/isolate_patch.dart:84)
  #4      _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:131)
  </code></pre>