Fix first-day-of-week detexion in dense calculator (Upcoming Transact…

…ions)

GnuCash depends on GTK3, and not GTK2. Thus:
  $ gettext -d gtk20 calendar:week_start:0; echo
  calendar:week_start:0
  $ LC_LANG=pl_PL.UTF-8 gettext -d gtk20 calendar:week_start:0; echo
  calendar:week_start:0

  $ gettext -d gtk30 calendar:week_start:0; echo
  calendar:week_start:1
  $ LC_LANG=pl_PL.UTF-8 gettext -d gtk30 calendar:week_start:0; echo
  calendar:week_start:1
because the "gtk20" catalog, provided by GTK2, doesn't exist.

Fixes: https://bugs.gnucash.org/show_bug.cgi?id=797623
Fixes: https://bugs.gnucash.org/show_bug.cgi?id=752395

gnucash/gnome-utils/gnc-dense-cal.c

@@ -505,9 +505,9 @@ gnc_dense_cal_init(GncDenseCal *dcal)
            string into the gnucash.pot file when calling xgettext. */
 #define dgettext_noextract dgettext
         /* Translators: This string must not show up in gnucash.pot as
-           it is looked up in the "gtk20" translation domain
+           it is looked up in the "gtk30" translation domain
            instead. */
-        week_start_str = dgettext_noextract("gtk20", "calendar:week_start:0");
+        week_start_str = dgettext_noextract("gtk30", "calendar:week_start:0");
 #undef dgettext_noextract
 
         parts = g_strsplit(week_start_str, ":", 3);