[ci] upgrade JRuby 9.2 to latest (9.2.6)

Author: kares

.travis.yml

@@ -59,20 +59,20 @@ matrix:
     - rvm: jruby-head
   include:
     # jruby-9.2
-    - rvm: jruby-9.2.5.0
+    - rvm: jruby-9.2.6.0
       env: DB=mysql2
-    - rvm: jruby-9.2.5.0
+    - rvm: jruby-9.2.6.0
       env: DB=postgresql
-    - rvm: jruby-9.2.5.0
+    - rvm: jruby-9.2.6.0
       env: DB=sqlite3
     # jruby-9.2 + Java 11
-    - rvm: jruby-9.2.5.0
+    - rvm: jruby-9.2.6.0
       env: DB=mysql2
       jdk: openjdk11
-    - rvm: jruby-9.2.5.0
+    - rvm: jruby-9.2.6.0
       env: DB=postgresql
       jdk: openjdk11
-    - rvm: jruby-9.2.5.0
+    - rvm: jruby-9.2.6.0
       env: DB=sqlite3
       jdk: openjdk11
     # jruby-head