Updated Ruby 2.7 on Travis

Author: kojix2

.travis.yml

@@ -24,6 +24,9 @@ matrix:
     - name: "Ruby trunk-nightly"
       env:
         - ruby_version=trunk-nightly
+    - name: "Ruby 2.7"
+      env:
+        - ruby_version=2.7.1
     - name: "Ruby 2.6"
       env:
         - ruby_version=2.6.5