.travis.yml in async-await-0.4.0 vs .travis.yml in async-await-0.5.0

@@ -5,9 +5,10 @@
   include:
     - rvm: 2.3
     - rvm: 2.4
     - rvm: 2.5
     - rvm: 2.6
+    - rvm: 2.7
     - rvm: 2.6
       env: COVERAGE=BriefSummary,Coveralls
     - rvm: ruby-head
     - rvm: jruby-head
     - rvm: truffleruby