Upgrade to roundcube 1.3.8

[JimboJoe]

See changelogs here:

• https://github.com/roundcube/roundcubemail/releases/tag/1.3.7
• https://github.com/roundcube/roundcubemail/releases/tag/1.3.8

[alexAubin]

Closing because current version is 1.3.8