Incorrect signature for generic type via `JavaType.getGenericSignature

(see https://github.com/FasterXML/jackson-modules-base/issues/8 for background)

It looks like generic signature generation is missing one closing `>` character to produce:

```
()Ljava/util/concurrent/atomic/AtomicReference<Ljava/lang/String;;
```

instead of expected

```
()Ljava/util/concurrent/atomic/AtomicReference<Ljava/lang/String;>;
```

that is, closing '>' is missing.
