upgrade to node-8 and to wiki-0.13.0

includes update to client and several plugins:
calendar, markdown, and html

Dockerfile

@@ -1,11 +1,12 @@
-FROM node:4-slim
+FROM node:8-slim
 
 RUN useradd --create-home app \
  && apt-get update \
  && apt-get install -y --no-install-recommends \
-    jq
+    jq \
+    git
 WORKDIR /home/app
-ARG WIKI_PACKAGE=wiki@0.12.1
+ARG WIKI_PACKAGE=wiki@0.13.0
 RUN su app -c "npm install -g --prefix . $WIKI_PACKAGE"
 RUN su app -c "mkdir .wiki"
 COPY configure-and-launch-wiki set-owner-name ./

README.md

@@ -52,8 +52,11 @@ Open http://that.localtest.me:3000 in another.
 
 # Development
 
+This image's tag matches the version of the included wiki software.
+
 ``` bash
-VERSION=0.12.0
-docker build --build-arg VERSION=$VERSION -t dobbs/farm:$VERSION .
-git tag -am "" $VERSION
+git tag -am "" '0.13.0'
+git push --tags
 ```
+
+The repos in Dockerhub and GitHub are configured to automatically build new tags.