Linter throw error when URL field in source is a list

[marcoesters]

Linter throws an error when URL is a list.

[bkreider]

Example: All of the R feedstocks have a list for source:

  url:
    - {{ cran_mirror }}/src/contrib/pkgdown_{{ version }}.tar.gz
    - {{ cran_mirror }}/src/contrib/Archive/pkgdown/pkgdown_{{ version }}.tar.gz

ERROR: /Users/bkreider/src/recipes/r-pkgdown-feedstock/recipe/meta.yaml:13: http_url: URL is the wrong data type. It should be a string. Got this instead: ['https://cloud.r-project.org/src/contrib/pkgdown_2.0.7.tar.gz', 'https://cloud.r-project.org/src/contrib/Archive/pkgdown/pkgdown_2.0.7.tar.gz'] is not https

[schuylermartin45]

Tracking: https://anaconda.atlassian.net/browse/PAT-182