Closes#6891.
This downgrades the get-stream package from 5.x to 4.x, which does not
use `async` functions which works around the problem of
`regeneratorRuntime` not being defined (it shouldn’t be needed).
This is an alternative solution to #6893 because I don’t know yet if we
want to enable `corejs` given that we will most likely drop support for
Node.js 8 and older in the next version.
Just like #6893 this PR comes without tests, but I verified locally that
`--stdin` works after this change.
Simon Lydell
9b1726d3cd