Upgrade docker image to python:3

Dockerfile

@@ -1,7 +1,12 @@
 #
 # Dockerfile for an alpine-based python container for python-vipaccess
 #
-FROM python:2.7-alpine
+# Create named image to make it easier to refer to
+#     "docker build . -t python-vipaccess"
+# Run vipaccess to generate tokens with 
+#     "docker run python-vipaccess provision -p"
+#
+FROM python:3-alpine
 
 LABEL maintainer "Kayvan Sylvan <kayvansylvan@gmail.com>"
 
@@ -11,8 +16,7 @@ WORKDIR /usr/src
 RUN apk add --no-cache --virtual .build-deps \
     gcc libc-dev libxml2-dev libxslt-dev \
   && apk add --no-cache libxml2 libxslt \
-  && pip install --no-cache-dir -r requirements.txt \
-  && pip install --no-cache-dir . \
+  && pip3 install --no-cache-dir . \
   && find /usr/local -name *.pyo -o -name *.pyc -exec rm -f '{}' \; \
   && apk del .build-deps && touch /root/.vipaccess