Use a newer macOS version to enable Reseek compilation

This PR tries to enable macOS builds by compiling Reseek in macOS 10.15

Please read the guidelines for Bioconda recipes before opening a pull request (PR).

General instructions

If this PR adds or updates a recipe, use "Add" or "Update" appropriately as the first word in its title.
New recipes not directly relevant to the biological sciences need to be submitted to the conda-forge channel instead of Bioconda.
PRs require reviews prior to being merged. Once your PR is passing tests and ready to be merged, please issue the @BiocondaBot please add label command.
Please post questions on Gitter or ping @bioconda/core in a comment.

Instructions for avoiding API, ABI, and CLI breakage issues

Conda is able to record and lock (a.k.a. pin) dependency versions used at build time of other recipes. This way, one can avoid that expectations of a downstream recipe with regards to API, ABI, or CLI are violated by later changes in the recipe. If not already present in the meta.yaml, make sure to specify run_exports (see here for the rationale and comprehensive explanation). Add a run_exports section like this:

build:
  run_exports:
    - ...

with ... being one of:

Case	run_exports statement
semantic versioning	`{{ pin_subpackage("myrecipe", max_pin="x") }}`
semantic versioning (0.x.x)	`{{ pin_subpackage("myrecipe", max_pin="x.x") }}`
known breakage in minor versions	`{{ pin_subpackage("myrecipe", max_pin="x.x") }}` (in such a case, please add a note that shortly mentions your evidence for that)
known breakage in patch versions	`{{ pin_subpackage("myrecipe", max_pin="x.x.x") }}` (in such a case, please add a note that shortly mentions your evidence for that)
calendar versioning	`{{ pin_subpackage("myrecipe", max_pin=None) }}`

while replacing "myrecipe" with either name if a name|lower variable is defined in your recipe or with the lowercase name of the package in quotes.

Bot commands for PR management

Please use the following BiocondaBot commands:

Everyone has access to the following BiocondaBot commands, which can be given in a comment:

`@BiocondaBot please update`	Merge the master branch into a PR.
`@BiocondaBot please add label`	Add the `please review & merge` label.
`@BiocondaBot please fetch artifacts`	Post links to CI-built packages/containers. You can use this to test packages locally.

Note that the @BiocondaBot please merge command is now depreciated. Please just squash and merge instead. Also, the bot watches for comments from non-members that include `@bioconda/` and will automatically re-post them to notify the addressed ``.

bioconda / bioconda-recipes