Update links in unic/README.md

[esoterra]

On the following page, the listed links are used but are not valid. They have an extra unic in them, which was probably correct before some refactor. https://github.com/open-i18n/rust-unic/blob/master/unic/README.md

• https://github.com/open-i18n/rust-unic/blob/master/unic/unic/ucd
• https://github.com/open-i18n/rust-unic/blob/master/unic/unic/bidi
• https://github.com/open-i18n/rust-unic/blob/master/unic/unic/normal
• https://github.com/open-i18n/rust-unic/blob/master/unic/unic/segment
• https://github.com/open-i18n/rust-unic/blob/master/unic/unic/idna
• https://github.com/open-i18n/rust-unic/blob/master/unic/unic/emoji

The only link which is currently correct is the first one in the README (unic-char).