* Fix MDX html parsing errors
For MDX wrap JSX parsing in a fragment before sending it of to babel for
parsing and formatting. In MDX adjacent JSX tags are permitted in the
root.
An option sent to the babel parser omits printing the root fragment and
instead just prints its children.
Solves #6943
* an attempt to address JounQin's comments
* use <$>...</$> instead of <>...</>
* refactoring
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.
JounQin