Update bootstrap.py to pull requirements from master branch

[roryk]

• I have read the guidelines for bioconda recipes.
• This PR adds a new recipe.
• AFAIK, this recipe is directly relevant to the biological sciences (otherwise, please submit to the more general purpose conda-forge channel).
• This PR updates an existing recipe.
• This PR does something else (explain below).

bootstrap.py wasn't working since it is trying to pull from the defunct cb3-migration branch; this updates it to pull from master. @bioconda/core ping for this one to get the thumbs up before merging.

[bgruening]

👍 :) Thanks @roryk!

[roryk]

Thanks!