vendor: update buildkit to v0.8

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

vendor/gopkg.in/yaml.v2/apic.go

@@ -86,6 +86,7 @@ func yaml_emitter_initialize(emitter *yaml_emitter_t) {
 		raw_buffer: make([]byte, 0, output_raw_buffer_size),
 		states:     make([]yaml_emitter_state_t, 0, initial_stack_size),
 		events:     make([]yaml_event_t, 0, initial_queue_size),
+		best_width: -1,
 	}
 }