[Alpine] Update Alpine base images to v3.13

data/Dockerfiles/dockerapi/Dockerfile

@@ -1,11 +1,17 @@
-FROM alpine:3.11
+FROM alpine:3.13
+
 LABEL maintainer "Andre Peters <andre.peters@servercow.de>"
 
 WORKDIR /app
 
-RUN apk add --update --no-cache python3 openssl tzdata \
- && pip3 install --upgrade pip \
- && pip3 install --upgrade docker flask flask-restful
+RUN apk add --update --no-cache python3 \
+  py3-pip \
+  openssl \
+  tzdata \
+&& pip3 install --upgrade pip \
+  docker \
+  flask \
+  flask-restful
 
 COPY dockerapi.py /app/