.travis.yml in ruby-nmap-0.9.3 vs .travis.yml in ruby-nmap-0.10.0

@@ -1,11 +1,13 @@
 language: ruby
 before_install:
   - sudo apt-get install libxml2-dev libxslt1-dev
+  - gem update --system
+  - gem install bundler -v "~> 2.0"
 rvm:
-  - 2.1.9
-  - 2.2.4
-  - 2.3.1
+  - 2.5
+  - 2.6
+  - 2.7
   - jruby
   - rbx
 matrix:
   allow_failures:
     - rvm: jruby