It may help to use the doctor with -v

flutter doctor -v

for me the result was as

 ...
Flutter version 2.0.5 at /usr/local/Caskroom/flutter/2.0.5/flutter
...

Then fhe dart path can be set as

/usr/local/Caskroom/flutter/2.0.5/flutter/bin/cache/dart-sdk

It may help to use the doctor with -v

flutter doctor -v

for me the result was as

 ...
Flutter version 2.0.5 at /usr/local/Caskroom/flutter/2.0.5/flutter
...

Then the dart path can be set as

/usr/local/Caskroom/flutter/2.0.5/flutter/bin/cache/dart-sdk