我遵循Getting Started with Flutter指南，在运行实际的flutter命令时卡住了:
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.<anonymous closure> (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.<anonymous closure> (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.<anonymous closure> (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.<anonymous closure> (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.<anonymous closure> (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.<anonymous closure> (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)