use latest micromamba

repo2docker/buildpacks/conda/activate-conda.sh

@@ -7,7 +7,7 @@ if [[ "${KERNEL_PYTHON_PREFIX}" != "${NB_PYTHON_PREFIX}" ]]; then
     # if the kernel is a separate env, stack them
     # so both are on PATH, notebook first
     micromamba activate ${KERNEL_PYTHON_PREFIX}
-    micromamba activate ${NB_PYTHON_PREFIX} --stack
+    micromamba activate  --stack ${NB_PYTHON_PREFIX}
 
     # even though it's second on $PATH
     # make sure CONDA_DEFAULT_ENV is the *kernel* env

tests/conda/binder-dir/verify

@@ -5,6 +5,6 @@ from subprocess import check_output
 assert sys.version_info[:2] == (3, 5), sys.version
 
 out = check_output(["/tmp/bin/micromamba", "--version"]).decode("utf8").strip()
-assert out == "0.12.0", out
+assert out == "0.12.1", out
 
 import numpy