.travis.yml in isobib-0.4.3 vs .travis.yml in isobib-0.4.4

@@ -5,10 +5,12 @@
   - 2.5
   - 2.4
   - 2.3
   - ruby-head
 
-before_install: gem install bundler -v 1.16.1
+before_install:
+  - gem install bundler -v 2.0.1
+  - bundle update --bundler
 
 matrix:
   allow_failures:
     - rvm: ruby-head