Update CI with latest versions of ruby and redmine

.ruby-gemset

@@ -0,0 +1 @@
+redmine-tags

.travis.yml

@@ -5,30 +5,37 @@ services:
   - postgresql
 
 rvm:
-  - 2.3.8
-  - 2.4.5
-  - 2.5.3
+  - 2.4.10
+  - 2.5.9
+  - 2.6.7
+  - 2.7.3
 
 matrix:
   allow_failures:
     # Master may fail for any reason, on any ruby version.
     # It's good to keep an eye on it in case if fails because of us.
-    - rvm: 2.3.8
+    - rvm: 2.4.10
       env: REDMINE_VER=master DB=mysql
-    - rvm: 2.4.5
+    - rvm: 2.5.9
       env: REDMINE_VER=master DB=mysql
-    - rvm: 2.5.3
+    - rvm: 2.6.7
       env: REDMINE_VER=master DB=mysql
-    - rvm: 2.2.10
+    - rvm: 2.7.3
+      env: REDMINE_VER=master DB=mysql
+    - rvm: 2.4.10
       env: REDMINE_VER=master DB=postgresql
-    - rvm: 2.3.8
+    - rvm: 2.5.9
       env: REDMINE_VER=master DB=postgresql
-    - rvm: 2.4.5
+    - rvm: 2.6.7
       env: REDMINE_VER=master DB=postgresql
-    - rvm: 2.5.3
+    - rvm: 2.7.3
       env: REDMINE_VER=master DB=postgresql
 
 env:
+  - REDMINE_VER=4.2-stable DB=mysql
+  - REDMINE_VER=4.2-stable DB=postgresql
+  - REDMINE_VER=4.1-stable DB=mysql
+  - REDMINE_VER=4.1-stable DB=postgresql
   - REDMINE_VER=4.0-stable DB=mysql
   - REDMINE_VER=4.0-stable DB=postgresql
   - REDMINE_VER=master DB=mysql