[CI] Don't specify patch versions of Ruby

Author: picandocodigo

.ci/test-matrix.yml

@@ -3,10 +3,10 @@ ELASTICSEARCH_VERSION:
 - 7.x-SNAPSHOT
 
 RUBY_TEST_VERSION:
-- 2.7.0
-- 2.6.5
-- 2.5.7
-- 2.4.9
+- 2.7
+- 2.6
+- 2.5
+- 2.4
 
 TEST_SUITE:
 - oss

.travis.yml

@@ -28,23 +28,23 @@ matrix:
       jdk: oraclejdk8
       env: TEST_SUITE=client
 
-    - rvm: 2.7.0
+    - rvm: 2.7
       jdk: oraclejdk8
       env: TEST_SUITE=client
 
-    - rvm: 2.6.5
+    - rvm: 2.6
       jdk: oraclejdk8
       env: TEST_SUITE=client
 
-    - rvm: 2.5.7
+    - rvm: 2.5
       jdk: oraclejdk8
       env: TEST_SUITE=client
 
-    - rvm: 2.4.9
+    - rvm: 2.4
       jdk: oraclejdk8
       env: TEST_SUITE=client
 
-    - rvm: jruby-9.2.9.0
+    - rvm: jruby-9.2
       jdk: oraclejdk8
       env: TEST_SUITE=unit