Travis - use JDK 11

Travis output:

```
$ ~/bin/install-jdk.sh --target "/home/travis/oraclejdk12" --workspace "/home/travis/.cache/install-jdk" --feature "12" --license "BCL"
install-jdk.sh 2019-05-02
BCL licensed downloads are only supported up to JDK 11, but got: 12
```

Author: Vadim Platonov

.travis.yml

@@ -2,4 +2,4 @@ language: clojure
 lein: lein
 script: lein test-all
 jdk:
-  - oraclejdk12
+  - oraclejdk11