* formatting
* fix `typeof Symbol.prototype`
Babel uses a helper function to return the correct value for `typeof
obj` when obj is a Symbol and support for Symbol has been polyfilled.
This function assumes that `obj.constructor === Symbol` implies `typeof
obj === 'symbol'`.
This isn't true when obj is `Symbol.prototype`. In that case (REPL from
node 6, the same holds in Firefox):
```
> Symbol.prototype.constructor === Symbol
true
> typeof Symbol.prototype
'object'
>
```
AFAICS, that's the only case where the assumption doesn't hold.
The test added by this patch fails only on node 0.10, as 0.12 already
has a native implementation of Symbol and the polyfill code doesn't run.
This caused a problem in core-js when it's compiled with babel (the
issue was isolated by @skozin here:
https://github.com/zloirock/core-js/issues/189#issuecomment-209864582).
8f6d4ae5cf