Update itstool to 2.0.4

2.0.4
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* Fixed a massive performance issue

2.0.3
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* Added Python 3 support. Keeping Python 2 support for now. (Virgil Dupras)
* Fixed --keep-entities mode after some libxml2 changes.
* Added --path option for extra paths for ITS files.
* Don't error out (except under -s) for mismatched placeholders.
* Fixed UTF-8 handling for translated attributes.

(prlw1)