Bug 30252: lower version of 'Locale::XGettext::TT2' to 0.6

Bug 30252: lower version of 'Locale::XGettext::TT2' to 0.6

this patch reduces the required version of 'Locale::XGettext::TT2' to 0.6

version 0.7 of of Locale::XGettext::TT2 is incompatible with the current version of libintl-perl (1.26), so we use 0.6 instead

 https://packages.debian.org/stretch/libintl-perl
 https://metacpan.org/release/GUIDO/Template-Plugin-Gettext-0.6/view/lib/Locale/XGettext/TT2.pm

we will move to 'Locale::XGettext::TT2' 0.7 when libintl-perl-1.32 arrives
 https://tracker.debian.org/pkg/libintl-perl

small change, no test plan

Signed-off-by: Mason James <mtj@kohaaloha.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>