fix hashUID function

[bebbi]

hashing UID works but is not completely following specs
http://www.itu.int/rec/T-REC-X.667-201210-I/en
The sha1.js might be returning wrong sha1 functions for strings that contain non-readable chars.
Also, the final replacement of digits may be wrong.
Issue appears minor, but there's an unknown risk of the sha1.js reducing the target value space, so better to implement and confirm compliance with specs.