Update Dockerfile to use the alpine Python 3 base image

Dockerfile

@@ -1,4 +1,4 @@
-FROM python:3-slim
+FROM python:alpine
 
 ENV DRYRUN 'True'
 ENV DEBUG 'True'
@@ -32,13 +32,8 @@ ENV WHITELIST_USERS  ''
 
 WORKDIR /app
 
-RUN apt-get update && \
-    apt-get install -y --no-install-recommends \
-        build-essential && \
-    apt-get clean && \
-    rm -rf /var/lib/apt/lists/*
-
 COPY ./requirements.txt ./
+
 RUN pip install --no-cache-dir -r requirements.txt
 
 COPY . .