Add testing on OpenJDK 15

.travis.yml

@@ -90,6 +90,8 @@ matrix:
       install: . ./install-jdk.sh -F 13 -L GPL
     - env: JDK='OpenJDK 14'
       install: . ./install-jdk.sh -F 14 -L GPL
+    - env: JDK='OpenJDK 15'
+      install: . ./install-jdk.sh -F 15 -L GPL
 
 before_install:
   - mv .travis/settings.xml $HOME/.m2/settings.xml

readme.md

@@ -35,7 +35,7 @@ Builds/tests
 
 [![Travis-CI Build Status](https://api.travis-ci.org/moparisthebest/JdbcMapper.svg?branch=master)](https://travis-ci.org/moparisthebest/JdbcMapper)
 
-JdbcMapper is currently built and tested using travis-ci on every version of Java 6 to 13, and against all 
+JdbcMapper is currently built and tested using travis-ci on every version of Java 6 to 15, and against all
 databases/drivers that could be found, currently [MariaDB](https://mariadb.org) ([MySQL](https://www.mysql.com/)), 
 [PostgreSQL](https://www.postgresql.org/), [Oracle](https://www.oracle.com/database/technologies/appdev/xe.html), 
 [MS-SQL](https://www.microsoft.com/en-us/sql-server), [SQLite](https://sqlite.org), [H2](https://www.h2database.com/),