Bug in Hex conversion

Hello @hustcc 👋

I using `radix.js version 0.0.1`. I wanted to convert a hex value to an octal. This is my code:
```
let hexValue = ans = undefined

hexValue = "1F4"
ans = radix.convent(hexValue, 16, 8);
console.log(ans)

// Output: 364
```

**ISSUE:**
The program outputs *octal value* `364`. But the actual octal value of hex 1F4 is `764`.

----

Then I modified my code this way:
```
let hexValue = ans = undefined

hexValue = "1F4"
hexValue = hexValue.toLowerCase() // [Modified line] Make uppercase hex letters to lowercase

ans = radix.convent(hexValue, 16, 8);
console.log(ans)

// Output: 764
```

Now this time the program prints out the expected output 👍. I also tested hex with the other radices. The issues exist with the following conversions:

* Hex => Octal
* Hex => Bin
* Hex => Dec

> Conclusion: So I think this issue will be fixed if you convert the hex letters to lowercase and then doing the conversion.

 
Thanks.