Update geckodriver + Firefox versions (#133)

* Update geckodriver + Firefox versions

* Use latest Firefox build/version

.travis.yml

@@ -3,7 +3,7 @@ python:
   - 2.7
   - 3.6
 addons:
-  firefox: 53.0
+  firefox: latest
 env:
   global:
     - DISPLAY=:99.0
@@ -21,7 +21,7 @@ matrix:
     - python: 2.7
     - python: 3.6
 before_install:
-  - wget -O geckodriver.tar.gz https://github.com/mozilla/geckodriver/releases/download/v0.16.1/geckodriver-v0.16.1-linux64.tar.gz
+  - wget -O geckodriver.tar.gz https://github.com/mozilla/geckodriver/releases/download/v0.18.0/geckodriver-v0.18.0-linux64.tar.gz
   - gunzip -c geckodriver.tar.gz | tar xopf -
   - chmod +x geckodriver && sudo mv geckodriver /usr/local/bin
   - firefox --version