Small improvement

build.docker-compose.yml

@@ -2,7 +2,7 @@ version: '2'
 services:
   squidex-build:
 # Use custom aspnet images where phantomjs is installed
-    image: sebastianstehle/aspnetcore-build:1.1.0-projectjson-phantomjs
+    build: tools/aspnetcore-build-phantomjs
     volumes:
       - .:/sln
     working_dir: /sln

tools/aspnetcore-build-phantomjs/Dockerfile

@@ -0,0 +1,27 @@
+FROM microsoft/aspnetcore-build:1.1.0-projectjson
+	
+# Install runtime dependencies
+RUN apt-get update \
+ && apt-get install -y --no-install-recommends ca-certificates bzip2 libfontconfig \
+ && apt-get clean \
+ && rm -rf /var/lib/apt/lists/*
+ 
+ # Install official PhantomJS release
+RUN set -x  \
+ && apt-get update \
+ && apt-get install -y --no-install-recommends \
+ && mkdir /srv/var \
+ && mkdir /tmp/phantomjs \
+   # Download Phantom JS
+ && curl -L https://bitbucket.org/ariya/phantomjs/downloads/phantomjs-2.1.1-linux-x86_64.tar.bz2 | tar -xj --strip-components=1 -C /tmp/phantomjs \
+   # Copy binaries only
+ && mv /tmp/phantomjs/bin/phantomjs /usr/local/bin \
+   # Create symbol link
+   # Clean up
+ && apt-get autoremove -y \
+ && apt-get clean all \
+ && rm -rf /tmp/* /var/lib/apt/lists/*
+
+RUN phantomjs --version
+
+WORKDIR /