remove unused build arg

Author: hekra

docker/Dockerfile

@@ -1,31 +1,27 @@
 # Dockerfile to build a Webdriver for QT5
-# Check port mapping when running the container
-# e.g:
-# $ docker build --rm=true --no-cache -t latest:latest docker/
-# $ docker run -ti --rm -p 9531:9517 latest:latest --verbose
+# Documentation: https://github.com/cisco-open-source/qtwebdriver/wiki/Docker
 
 FROM  alexzaporozhets/ubuntu-qt5.4.2
 MAINTAINER Hugues Ekra <hekra@cisco.com>
 LABEL vendor="Cisco Systems"
 LABEL license="LGPLv2.1"
 LABEL version="1.3.3"
 
-# Args
-ARG QPA_PLATFORM
-
 #Env
 ENV QTDIR "/opt/Qt5.4.2/5.4/gcc_64"
 ENV QT_PLUGIN_PATH $QTDIR/plugins
-ENV QT_QPA_PLATFORM ${QPA_PLATFORM:-offscreen}
+ENV QT_QPA_PLATFORM offscreen
 ENV QT_QPA_FONTDIR /opt/Qt5.4.2/5.4/Src/qtbase/lib/fonts
 WORKDIR /opt
 
 # Build
 RUN echo 'debconf debconf/frontend select Noninteractive' | debconf-set-selections \
     && sudo apt-get update && sudo apt-get install -y \
-        g++ gyp xvfb libicu-dev libegl1-mesa-dev libgles2-mesa-dev \
+        g++ gyp xvfb xorg libicu-dev libegl1-mesa-dev libgles2-mesa-dev \
     && wget https://github.com/cisco-open-source/qtwebdriver/archive/WD_1.X_dev.zip \
-    && unzip WD_1.X_dev.zip && mv qtwebdriver-WD_1.X_dev qtwebdriver && cd qtwebdriver \
+    && unzip WD_1.X_dev.zip \
+    && mv qtwebdriver-WD_1.X_dev qtwebdriver \
+    && cd qtwebdriver \
     && cp ./qt5_sample_config.gypi ./wd.gypi \
     && sed -i "s@\/home\/hekra01\/qt@$QTDIR@g" wd.gypi \
     && ./build.sh