Update latest gemfile for Travis

Author: lcreid

test/gemfiles/6.0.gemfile

@@ -6,12 +6,14 @@ gem "rails", "~> 6.0.0.rc1"
 
 group :development do
   gem "rubocop", require: false
+  gem "sass-rails"
+  gem 'webpacker', '>= 4.0.0.rc.3'
 end
 
 group :test do
   gem "diffy"
   gem "equivalent-xml"
   gem "mocha"
-  gem "sqlite3", "~> 1.3.6"
+  gem "sqlite3"
   gem "timecop", "~> 0.7.1"
 end