Yams: repair the build with the autodifferentiation toolchain
Yams: repair the build with the autodifferentiation toolchain

```
error: static member 'pow' cannot be used on instance of type 'Double'
```

When building Yams with the TensorFlow toolchain, this crops us.  Simply
add the explicit type annotation.

jpsim/Yams,jpsim/Yams,jpsim/Yams