fix missing dependency

[h-vetinari]

Encountered in a local render after #181 / #182:

  [...]
  File "C:\Users\[...]\.conda\envs\builder\lib\site-packages\conda_build\metadata.py", line 1546, in _get_contents
    from conda_build.jinja_context import context_processor, UndefinedNeverFail, FilteredLoader
  File "C:\Users\[...]\.conda\envs\builder\lib\site-packages\conda_build\jinja_context.py", line 13, in <module>
    import toml
ModuleNotFoundError: No module named 'toml'

[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.

[isuruf]

Thanks