meson.build: Reflect usage of 0.59 Meson features

src/fe-gtk/meson.build calls feature_opt.allowed() which wasn't
added until 0.59.

Signed-off-by: Christopher Byrne <salah.coronya@gmail.com>
(cherry picked from commit 5018a3a848)

meson.build

@@ -1,6 +1,6 @@
 project('zoitechat', 'c',
   version: run_command('cat', 'VERSION', check: true).stdout().strip(),
-  meson_version: '>= 0.55.0',
+  meson_version: '>= 0.59.0',
   default_options: [
     'c_std=c17',
     'buildtype=debugoptimized',