normaliseHamza() converts numbers to letters

**Example Usage**
`
        echo $arabic->normaliseHamza("10 ش أحمد عصمت");
`
**Expected Output**
`
        10 ش احمد عصمت
`
**Generated Output**
`
يو ش احمد عصمت
`

Apparently, 0 converts to 'و' and 1 converts to 'ي'. I have tried other numbers and they do not generate this bug, only 1 and 0.