ci(travis): change build dist to trusty and remove bundler script (#49)

.travis.yml

@@ -1,16 +1,6 @@
+dist: trusty
 language: ruby
 bundler_args: --without development
-before_install:
-  # Extracts the ruby version number
-  - RUBY_VERS="$(bc -l<<<$(ruby -v | cut -d' ' -f 2 | cut -d'.' -f 1,2))"
-  # Bundler 2.0 requires at least ruby vers 2.3.0
-  - LATEST_VERS=2.3
-  # Based on a given job's ruby version, install either
-  # Bundler 2.x or 1.17
-  - if (( $(echo "$RUBY_VERS >= $LATEST_VERS" | bc -l) ));
-      then echo $(gem install bundler); 
-      else echo $(gem install bundler -v '< 2'); 
-    fi
 rvm:
   - 2.3.0
   - 2.2.4