meson: Use proper type for bools

Fix invalid usage of bools which violates official meson specification and thus
breaks muon, an implementation of meson written in C.

Signed-off-by: illiliti <illiliti@protonmail.com>

meson_options.txt

@@ -1,23 +1,23 @@
 option('libraries',
   description: 'Compile Wayland libraries',
   type: 'boolean',
-  value: 'true')
+  value: true)
 option('scanner',
   description: 'Compile wayland-scanner binary',
   type: 'boolean',
-  value: 'true')
+  value: true)
 option('tests',
   description: 'Compile Wayland tests',
   type: 'boolean',
-  value: 'true')
+  value: true)
 option('documentation',
   description: 'Build the documentation (requires Doxygen, dot, xmlto, xsltproc)',
   type: 'boolean',
-  value: 'true')
+  value: true)
 option('dtd_validation',
   description: 'Validate the protocol DTD (requires libxml2)',
   type: 'boolean',
-  value: 'true')
+  value: true)
 option('icon_directory',
   description: 'Location used to look for cursors (defaults to ${datadir}/icons if unset)',
   type: 'string',