"fix" for utils/expressions/"^" rule not displaying zero exponent expressions

It's currently not possible to express expressions with zero exponents:

```
expr(["^", "a", 0]) 
```

results in <code>""</code>. I suppose I could put the zero in quotes, but that doesn't help with variables, right?

It seems clear that the "if pow === 0" check was put in there for a reason, so I'm fairly confident that my "fix" is in conflict with something else (hence the quotes).