具体错误信息如下：
错误一：
Error on line 6, column 5 of pubspec.yaml: A dependency may only have one source.
sdk: flutter^^^^^^^^^^^^^
pub upgrade failed (65)
错误二：
Error on line 6, column 8 of pubspec.yaml: Invalid version constraint: Could not parse version "flutter". Unknown text at "flutter".
sdk: flutter^^^^^^^
pub upgrade failed (65)
此时，注意 pubspec.yaml 文件添加依赖的内容，特别注意 sdk 对齐格式。正确格式如下图所示：
