Travis: test 5.5 and 5.6, drop 5.6
Travis: test 5.5 and 5.6, drop 5.6
mozilla-l10n/webdashboard,flodolo/webdashboard,pascalchevrel/webdashboard,pascalchevrel/webdashboard,flodolo/webdashboard,mozilla-l10n/webdashboard,flodolo/webdashboard,mozilla-l10n/webdashboard