Fix pull request failures

[chrisburr]

Since #44, pull requests builds are currently failing on platforms other than azure due to BINSTAR_TOKEN not being set. Example from this build:

+ upload_package /home/conda/feedstock_root /home/conda/recipe_root /home/conda/feedstock_root/.ci_support/linux_python3.7.yaml
Traceback (most recent call last):
  File "/opt/conda/bin/upload_package", line 11, in <module>
    sys.exit(upload_package())
  File "/opt/conda/lib/python3.6/site-packages/click/core.py", line 764, in __call__
    return self.main(*args, **kwargs)
  File "/opt/conda/lib/python3.6/site-packages/click/core.py", line 717, in main
    rv = self.invoke(ctx)
  File "/opt/conda/lib/python3.6/site-packages/click/core.py", line 956, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/opt/conda/lib/python3.6/site-packages/click/core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "/opt/conda/lib/python3.6/site-packages/conda_forge_ci_setup/build_utils.py", line 82, in upload_package
    upload_or_check(recipe_root, owner, channel, [config_file])
  File "/opt/conda/lib/python3.6/site-packages/conda_forge_ci_setup/upload_or_check_non_existence.py", line 95, in upload_or_check
    if token.startswith('$('):
AttributeError: 'NoneType' object has no attribute 'startswith'

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe) and found it was in an excellent condition.

[chrisburr]

Of course, the CI fails due to the bug this fixes... 😆

[mariusvniekerk]

The ci is fetching this file from master so it's broken

[mariusvniekerk]

We should just merge this