HADOOP-16151. pip install pylint fails in branch-2.8 and branch-2.9.

Contributed by Akira Ajisaka.

dev-support/docker/Dockerfile

@@ -122,6 +122,7 @@ RUN apt-get -q install --no-install-recommends -y bats
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 # Install pylint
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+RUN pip install isort==4.3.8
 RUN pip install pylint==1.9.2
 
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