Update .travis.yml to use latest Firefox version

Author: acrellin

.travis.yml

@@ -54,11 +54,11 @@ addons:
     - supervisor
     - nginx
     - xvfb
-    - firefox
     - unzip
     - libnss3
     - libgconf-2-4
   postgresql: "9.6"
+  firefox: latest
 
 matrix:
   include:

.travis/travis_install.sh

@@ -4,8 +4,9 @@ set -ex
 
 section "install.base.requirements"
 
-# Check Firefox version
+# Check Firefox & GeckoDriver versions
 firefox --version
+geckodriver --version
 
 # Install v1.7 or newer of nginx to support 'if' statement for logging
 sudo apt-add-repository -y ppa:nginx/development