Use newMemoryDirectDB instead of newDirectMemoryDB

Hi,

I cannot create a producer now. The exception says:

```
Exception in thread "main" java.lang.ExceptionInInitializerError
        at clojure.main.<clinit>(main.java:20)
Caused by: java.lang.NoSuchFieldException: newDirectMemoryDB, compiling:(kafka_clj/msg_persist.clj:102:21)
```

Traced this back to this rename
https://github.com/jankotek/MapDB/commit/3d7a6fbfa18922385918976c9de1a73ce180f6bc