.travis.yml in pesapal-1.6.0 vs .travis.yml in pesapal-1.7.0

- old
+ new

@@ -1,8 +1,10 @@
 language: ruby
+before_install:
+  - gem update --system
+  - gem install bundler
 rvm:
-  - 2.1.2
-  - 2.1.1
-  - 2.1.0
-  - 2.0.0
-  - 1.9.3
+  - 2.3
+  - 2.2
+  - 2.1
+  - 2.0
 script: bundle exec rspec spec