Update krona recipe to extended-base image

[skrakau]

Use extended-base image for Krona to allow download when using Singularity (see also #11583).

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[skrakau]

@BiocondaBot please fetch artifacts

[BiocondaBot]

Package(s) built on CircleCI are ready for inspection:

Arch	Package	Repodata
noarch	krona-2.7.1-pl526_5.tar.bz2	repodata.json
noarch	krona-2.8-pl526_1.tar.bz2	repodata.json

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You may also use conda to install these:

• For packages on noarch:

conda install -c https://143696-42372094-gh.circle-artifacts.com/0/tmp/artifacts/packages <package name>

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Docker image(s) built:

Package	Tag	Install with docker
krona	2.7.1--pl526_5	show curl "https://143696-42372094-gh.circle-artifacts.com/0/tmp/artifacts/images/krona%3A2.7.1--pl526_5.tar.gz" | gzip -dc | docker load
krona	2.8--pl526_1	show curl "https://143696-42372094-gh.circle-artifacts.com/0/tmp/artifacts/images/krona%3A2.8--pl526_1.tar.gz" | gzip -dc | docker load

[skrakau]

@BiocondaBot please add label

[dpryan79]

@bioconda-bot please merge

[BiocondaBot]

I will attempt to upload artifacts and merge this PR. This may take some time, please have patience.