Bump drush version

[martinfrances107]

No description provided.

[martinfrances107]

currently the drush version is

"drush/drush:^9.0.0-beta4"

I have filed a series of micro issues ... this is a low priority ... I will try and get to this at the end

The current beta is 9.0.0-beta9

I am a fan of small and frequent maintenance ... so this is a nice thing to have....

[martinfrances107]

#33 is a pull request which updates to 9.0.0-beta9

I have tested this by running .dropwhale/reset.sh

which get drush and then runs drush sites install

I then did a .dropwhale/bash.sh

and looked at composer.json to confirm that the correct drush was in place.

I think this PR is a complete solution to the issue.