Update to new libxkbcommon API

We no longer depend on xproto, we use xkbcommon keycodes now. Yay!
diff --git a/src/compositor-x11.c b/src/compositor-x11.c
index dca2324..0777d77 100644
--- a/src/compositor-x11.c
+++ b/src/compositor-x11.c
@@ -737,7 +737,7 @@
 	length_part = strlen(value_part); \
 	if (value_part + length_part > (value_all + length_all) && \
 	    length_part > 0 && c->base.xkb_info.names.to == NULL) { \
-		free(c->base.xkb_info.names.to); \
+		free((char *) c->base.xkb_info.names.to);	    \
 		c->base.xkb_info.names.to = strdup(value_part); \
 	} \
 	value_part += length_part + 1;