メモ : heroku docker:start でflag provided but not defined: --file と言われたらboot2dockerが古い

掲題のとおりです

現象

$ heroku docker:start flag provided but not defined: --file

... 
building image...
 !    Error: Command failed: docker build --force-rm --file="...
...
flag provided but not defined: --file

Usage: docker build [OPTIONS] PATH | URL | -
...

対処

$ boot2docker upgrade 

でいけるはず、、