update to geckodriver 0.15

Author: ddavison

NodeFirefox/Dockerfile

@@ -25,7 +25,7 @@ RUN apt-get update -qqy \
 #============
 # GeckoDriver
 #============
-ARG GECKODRIVER_VERSION=0.14.0
+ARG GECKODRIVER_VERSION=0.15.0
 RUN wget --no-verbose -O /tmp/geckodriver.tar.gz https://github.com/mozilla/geckodriver/releases/download/v$GECKODRIVER_VERSION/geckodriver-v$GECKODRIVER_VERSION-linux64.tar.gz \
   && rm -rf /opt/geckodriver \
   && tar -C /opt -zxf /tmp/geckodriver.tar.gz \