meson.build: Fix the version format

The current version is prefixed by a "v" and therefore breaks the output
of "swaymsg -rt get_version" which is implemented trough
"sscanf(SWAY_VERSION, "%u.%u.%u", &major, &minor, &patch)".

The prefixed "v" was added in 8b2ff2f1, probably by accident.

meson.build

@@ -1,7 +1,7 @@
 project(
 	'sway',
 	'c',
-	version: 'v1.5', #release_version
+	version: '1.5', #release_version
 	license: 'MIT',
 	meson_version: '>=0.53.0',
 	default_options: [