Hyperspec to_js method broken

```ruby
def to_js(*args, &block)
opal_compile(*process_params(*args, &block))
end
```
needs to be
```
def to_js(*args, &block)
opal_compile(process_params(*args, &block).first)
end
```
(second value from process_params is options for mounting, which opal_compile doesn't need)

Should have a simple spec anyway that says yes I returned a string with length > 0