add 2.5.0 to travis ruby versions

Author: valich

.travis.yml

@@ -11,7 +11,7 @@ rvm:
   - 2.2.8
   - 2.3.5
   - 2.4.2
-  - 2.5.0-preview1
+  - 2.5.0
   - ruby-head
 
 matrix:
@@ -24,8 +24,6 @@ matrix:
       rvm: 1.9.3
     - os: osx
       rvm: 2.0.0
-    - os: linux
-      rvm: 2.5.0-preview1
 
 #  include:
 #    - os: osx