meson: Make cairo mandatory

We use cairo all around the codebase unconditionally, yet for some
reason it was an optional dependency.

Cc: Petri Latvala <petri.latvala@intel.com>
Signed-off-by: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Acked-by: Petri Latvala <petri.latvala@intel.com>
diff --git a/meson.build b/meson.build
index 9036feb..509ae5d 100644
--- a/meson.build
+++ b/meson.build
@@ -47,7 +47,7 @@
 	config.set('HAVE_VALGRIND', 1)
 endif
 
-cairo = dependency('cairo', version : '>1.12.0', required : false)
+cairo = dependency('cairo', version : '>1.12.0', required : true)
 
 libudev = dependency('libudev', required : false)
 if libudev.found()