Fix poetry's installer packaging for Linux

Makefile

@@ -55,6 +55,7 @@ linux_release:
 		-e PYTHON36=/opt/python/cp36-cp36m/bin/python \
 		-e PYTHON37=/opt/python/cp37-cp37m/bin/python \
 		-e PYTHON38=/opt/python/cp38-cp38/bin/python \
+		-e PYTHON39=/opt/python/cp39-cp39/bin/python \
 		quay.io/pypa/manylinux2010_x86_64 sh -c "cd /io && ./make-nix-release.sh"
 
 # run tests against all supported python versions

make-nix-release.sh

@@ -3,13 +3,13 @@
 set -e
 
 test -n "$PYTHON" || PYTHON="python3"
-$PYTHON -m pip install pip -U
-$PYTHON -m pip install poetry -U --pre
-$PYTHON -m poetry config virtualenvs.create false
-$PYTHON -m poetry install --no-dev
-$PYTHON sonnet make release \
+$PYTHON get-poetry.py -y
+$PYTHON $HOME/.poetry/bin/poetry config virtualenvs.create false
+$PYTHON $HOME/.poetry/bin/poetry install --no-dev
+$PYTHON $HOME/.poetry/bin/poetry run python sonnet make release \
     ${PYTHON27:+-P "2.7:$PYTHON27"} \
     ${PYTHON35:+-P "3.5:$PYTHON35"} \
     ${PYTHON36:+-P "3.6:$PYTHON36"} \
     ${PYTHON37:+-P "3.7:$PYTHON37"} \
-    ${PYTHON38:+-P "3.8:$PYTHON38"}
+    ${PYTHON38:+-P "3.8:$PYTHON38"} \
+    ${PYTHON39:+-P "3.9:$PYTHON39"}