libjvm.so is looked for in the wrong place

On travis, even with `JAVA_HOME` set, the library is not found.

It is actually in:

```
/usr/lib/jvm/java-8-openjdk-amd64/jre/lib/amd64/server/libjvm.so
```

But pyjnius looks in:

```
/usr/lib/jvm/java-8-openjdk-amd64/jre/lib/server/libjvm.so
```
