Install PhantomJS 2.1.1 on Travis-CI

I've found it to be much more stable locally - hopefully it will help
with our flaky CI issues (#901).

Code mostly cargo-culted from
9d3afe3d04

.travis.yml

@@ -1,6 +1,9 @@
 sudo: false
 language: ruby
-cache: bundler
+cache:
+  bundler: true
+  directories:
+    - travis_phantomjs
 env:
   matrix:
     - GROWSTUFF_SITE_NAME="Growstuff (travis)" RAILS_SECRET_TOKEN='xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx' GROWSTUFF_ELASTICSEARCH='true'
@@ -9,6 +12,12 @@ env:
     secure: "Z5TpM2jEX4UCvNePnk/LwltQX48U2u9BRc+Iypr1x9QW2o228QJhPIOH39a8RMUrepGnkQIq9q3ZRUn98RfrJz1yThtlNFL3NmzdQ57gKgjGwfpa0e4Dwj/ZJqV2D84tDGjvdVYLP7zzaYZxQcwk/cgNpzKf/jq97HLNP7CYuf4="
 rvm:
 - 2.3.1
+before_install:
+  - export PATH=$PWD/travis_phantomjs/phantomjs-2.1.1-linux-x86_64/bin:$PATH
+  - if [ $(phantomjs --version) != '2.1.1' ]; then rm -rf $PWD/travis_phantomjs; mkdir -p $PWD/travis_phantomjs; fi
+  - if [ $(phantomjs --version) != '2.1.1' ]; then wget https://assets.membergetmember.co/software/phantomjs-2.1.1-linux-x86_64.tar.bz2 -O $PWD/travis_phantomjs/phantomjs-2.1.1-linux-x86_64.tar.bz2; fi
+  - if [ $(phantomjs --version) != '2.1.1' ]; then tar -xvf $PWD/travis_phantomjs/phantomjs-2.1.1-linux-x86_64.tar.bz2 -C $PWD/travis_phantomjs; fi
+  - phantomjs --version
 before_script:
 - psql -c 'create database growstuff_test;' -U postgres
 script:

Gemfile

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 source 'https://rubygems.org'
 
 ruby '2.3.1'
@@ -14,11 +15,11 @@ gem 'haml'
 gem 'bootstrap-sass', '~> 3.3.6'
 gem 'font-awesome-sass'
 
-gem 'uglifier', '~> 2.7.2'         # JavaScript compressor
+gem 'uglifier', '~> 2.7.2' # JavaScript compressor
 
 gem 'jquery-rails'
 gem 'jquery-ui-rails', '~> 5.0.2'
-gem 'js-routes'  # provides access to Rails routes in Javascript
+gem 'js-routes' # provides access to Rails routes in Javascript
 gem 'flickraw'
 
 gem 'leaflet-rails'
@@ -68,7 +69,7 @@ gem 'omniauth-flickr', '>= 0.0.15'
 gem 'omniauth-facebook'
 
 # client for Elasticsearch. Elasticsearch is a flexible
-# and powerful, distributed, real-time search and analytics engine. 
+# and powerful, distributed, real-time search and analytics engine.
 # An example of the use in the project is fuzzy crop search.
 gem "elasticsearch-model"
 gem "elasticsearch-rails"
@@ -80,7 +81,7 @@ group :production, :staging do
   gem 'dalli'
   gem 'memcachier'
   gem 'rails_12factor' # supresses heroku plugin injection
-  gem 'bonsai-elasticsearch-rails'  # Integration with Bonsa-Elasticsearch on heroku
+  gem 'bonsai-elasticsearch-rails' # Integration with Bonsa-Elasticsearch on heroku
   gem 'sparkpost_rails'
 end