Mistake in extreme conditions

```javascript
var safeFloat = require("safe-float")
safeFloat.minus('10000000000000000000000000000000000000000', '1')
```
> "1e+40"

```javascript
var safeFloat = require("safe-float")
safeFloat.minus('1.00011010101010101', '0.000000000000000000000000000001')
```
> "1.000000000001.1010101010101e+26"

Both of them above are incorrect.