Update GUIDELINES.md

[lecorguille]

fix url

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• 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).

It just fixes an url

[dpryan79]

Thanks for catching this!