Added git install to Dockerfile

This is needed in order to install the forked repo `djangorestframework-camelizer` from github

Dockerfile

@@ -18,6 +18,8 @@ RUN apk update \
   && apk add --virtual build-deps gcc python3-dev musl-dev curl \
   && apk add --no-cache postgresql-dev
 
+RUN apk add --no-cache git
+
 COPY requirements.txt .
 RUN pip install -r requirements.txt && rm -rf /root/.cache