alias python=python3.7 for armv7

apt's version of numpy is for python 3.7.

And it doesn't work with python 3.8.

So I guess we're gonna have to downgrade to python 3.7 on armv7.

Dockerfile

@@ -31,6 +31,7 @@ RUN DEBIAN_FRONTEND=noninteractive apt-get install -qq -y --fix-missing --no-ins
   && if [ "$TARGETPLATFORM" = "linux/arm/v7" ]; then \
         apt-get -y install python-pandas; \
         sed -i '/pandas/d' requirements.txt; \
+        alias python=python3.7; \
      fi \
   && pip install -r requirements.txt \
   && pip cache purge \