Change image to ubuntu20.04

Dockerfile

@@ -1,13 +1,13 @@
-FROM python:3.9
+FROM ubuntu:20.04
 
 WORKDIR /code
 
 COPY ./requirements.txt /code/requirements.txt
 
 RUN apt-get update -qq && \
-    apt-get install -qq libfluidsynth build-essential libasound2-dev libjack-dev
+    apt-get install -qq python3-pip libfluidsynth build-essential libasound2-dev libjack-dev
 
-RUN pip install --no-cache-dir --upgrade -r /code/requirements.txt
+RUN pip3 install --no-cache-dir --upgrade -r /code/requirements.txt
 
 # Set up a new user named "user" with user ID 1000
 RUN useradd -m -u 1000 user
@@ -25,4 +25,4 @@ WORKDIR $HOME/app
 # Copy the current directory contents into the container at $HOME/app setting the owner to the user
 COPY --chown=user . $HOME/app
 
-CMD ["python", "main.py"]
+CMD ["python3", "main.py"]