Apply suggestions from code review - kou

Co-authored-by: Sutou Kouhei <kou@cozmixng.org>

Author: AlenkaF

ci/docker/conda-python-spark.dockerfile

@@ -30,8 +30,8 @@ RUN mamba install -q -y \
         openjdk=${jdk} \
         maven=${maven} \
         pandas && \
-    mamba clean --all
-RUN mamba uninstall -q -y numpy && \
+    mamba clean --all && \
+    mamba uninstall -q -y numpy && \
     /arrow/ci/scripts/install_numpy.sh ${numpy}
 
 # installing specific version of spark

ci/scripts/install_numpy.sh

@@ -19,7 +19,7 @@
 
 set -e
 
-if [ "$#" -lt 1 ]; then
+if [ $# -gt 1 ]; then
   echo "Usage: $0 <optional numpy version = latest>"
   exit 1
 fi