Update to ASM5 opscode.

If I include the following into my plugin classpath maven-plugin-pluging chokes. 
```xml
<dependency>
   <groupId>org.checkerframework</groupId>
   <artifactId>checker-qual</artifactId>
   <version>1.8.3</version>
</dependency>
```

Using ASM 5 opscodes in the visitor fixes the issue.