Fix Dockerfile (#172, #156)

This still doesn't work as expected, because `cht.sh.txt` runs in
interactive mode and gives the prompt.

    Where should cheat.sh be installed [/root/.cheat.sh]?

Dockerfile

@@ -1,13 +1,15 @@
-FROM alpine:latest
+FROM alpine:3.10
 WORKDIR /app
-COPY . /app
+COPY requirements.txt /app/
 RUN apk add --update --no-cache python2 py2-pip py2-gevent \
     py2-flask py2-requests py2-pygments py2-redis \
     py2-cffi py2-icu bash vim gawk sed \
     && apk add --no-cache --virtual build-deps python2-dev \
     build-base git \
     && pip install -r requirements.txt \
-    && sh share/scripts/get-sheets.sh \
     && apk del build-deps
+COPY . /app
+RUN apk add --update --no-cache curl git py2-virtualenv \
+    && ./share/cht.sh.txt --standalone-install
 ENTRYPOINT ["python2"]
 CMD ["bin/srv.py"]