Flutter在`flutter`命令上失败

我遵循Flutter入门指南，并在运行实际flutter命令时陷入困境：

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)