[CI] Update Ruby versions

Author: picandocodigo

.ci/test-matrix.yml

@@ -3,9 +3,9 @@ ELASTICSEARCH_VERSION:
 - 8.0.0-SNAPSHOT
 
 RUBY_TEST_VERSION:
+- 2.7.0
 - 2.6.5
 - 2.5.7
-- 2.4.9
 
 TEST_SUITE:
 - rest_api

.travis.yml

@@ -30,15 +30,15 @@ matrix:
       jdk: oraclejdk8
       env: TEST_SUITE=unit
 
-    - rvm: 2.6.5
+    - rvm: 2.7.0
       jdk: oraclejdk8
       env: TEST_SUITE=unit
 
-    - rvm: 2.5.7
+    - rvm: 2.6.5
       jdk: oraclejdk8
       env: TEST_SUITE=unit
 
-    - rvm: 2.4.9
+    - rvm: 2.5.7
       jdk: oraclejdk8
       env: TEST_SUITE=unit