[gimp] Fix GIMP_UNSTABLE macro. Fixes #5261.

[Jehan <jehanp src gnome org>]

commit 979b0bd9b309f8719099e1992b632ba2275b7052
Author: Félix Piédallu <fpiedallu kalrayinc com>
Date:   Mon Jul 6 10:55:05 2020 +0200

    Fix GIMP_UNSTABLE macro.
    Fixes #5261.

 meson.build | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/meson.build b/meson.build
index 01bb79441e..cd7569a6c2 100644
--- a/meson.build
+++ b/meson.build
@@ -65,7 +65,7 @@ conf.set_quoted('GETTEXT_PACKAGE', gettext_package)
 conf.set_quoted('GIMP_VERSION', gimp_version)
 
 stable = (gimp_app_version_minor % 2 == 0)
-conf.set10('GIMP_UNSTABLE', not stable)
+conf.set('GIMP_UNSTABLE', stable ? false : 1)
 
 versionconfig = configuration_data()
 versionconfig.set('GIMP_FULL_NAME',     full_name)