fix: use pip instead of pip3

Dockerfile

@@ -5,7 +5,7 @@ RUN apk add --update --no-cache python3 python3-dev build-base linux-headers pcr
 
 # Install pip, currently not needed, as installed by apk
 # RUN python3 -m ensurepip
-RUN pip3 install --no-cache --upgrade pip setuptools
+RUN pip install --no-cache --upgrade pip setuptools
 
 # Install dependencies
 COPY ./requirements.txt /app/requirements.txt