use "conda-forge" channel for mamba package

Author: rendner

Dockerfile

@@ -32,10 +32,10 @@ RUN mkdir "$pandas_home" \
 
 # Because it is surprisingly difficult to activate a conda environment inside a DockerFile
 # (from personal experience and per https://github.com/ContinuumIO/docker-images/issues/89),
-# we just update the base/root one from the 'environment.yml' file instead of creating a new one.
+# we just update the base/root from the 'environment.yml' file instead of creating a new one.
 #
 # Set up environment
-RUN conda install -y mamba
+RUN conda install -y -c conda-forge mamba
 RUN mamba env update -n base -f "$pandas_home/environment.yml"
 
 # Build C extensions and pandas