Use OpenJDK 8, add utPLSQL 3.1.8 to test matrix

Author: pesse

.travis.yml

@@ -5,7 +5,7 @@ services:
   - docker
 
 jdk:
-  - oraclejdk8
+  - openjdk8
 
 env:
   global:
@@ -32,6 +32,7 @@ env:
     - UTPLSQL_VERSION="v3.1.3"
     - UTPLSQL_VERSION="v3.1.6"
     - UTPLSQL_VERSION="v3.1.7"
+    - UTPLSQL_VERSION="v3.1.8"
     - UTPLSQL_VERSION="develop"
       UTPLSQL_FILE="utPLSQL"