[tex-live] libicu security update

[Karl Berry]

   https://security-tracker.debian.org/tracker/source-package/icu
   CVE ID         : CVE-2017-15422
   
   nb> Should TeX Live 2018 sources be updated to include the fix?

I suppose. Thanks. Following the links, it seems the diffs are at
https://ssl.icu-project.org/trac/changeset/40654

Akira, if you have time, could you install the changes? Else I will get
to it in a couple of days. --thanks, karl.