Use a similar download URL to those micromamba itself uses (#120)

The initial download of micromamba*.tar.bz2 from api.anaconda.org
has recently begun failing when run under docker, presumably due
to network setup changes elsewhere.

Instead use the same hostname and URL style as micromamba itself
uses when downloading and installing other packages, which does
still work when run from inside docker.

images/samtools/Dockerfile

@@ -7,7 +7,7 @@ ARG VERSION=${VERSION:-1.18}
 RUN apt-get update && apt-get install -y git wget bash bzip2 zip && \
     rm -r /var/lib/apt/lists/* && \
     rm -r /var/cache/apt/* && \
-    wget -qO- https://api.anaconda.org/download/conda-forge/micromamba/0.8.2/linux-64/micromamba-0.8.2-he9b6cbd_0.tar.bz2 | tar -xvj -C /usr/local bin/micromamba && \
+    wget -qO- https://conda.anaconda.org/conda-forge/linux-64/micromamba-0.8.2-he9b6cbd_0.tar.bz2 | tar -xvj -C /usr/local bin/micromamba && \
     mkdir ${MAMBA_ROOT_PREFIX} && \
     micromamba install -y --prefix ${MAMBA_ROOT_PREFIX} -c bioconda -c conda-forge \
     samtools=${VERSION} google-cloud-sdk dill && \