builder: Fix handling of VOLUME command where multiple volumes are

specified in a space delimited list.

Docker-DCO-1.1-Signed-off-by: Erik Hollensbe <github@hollensbe.org> (github: erikh)

builder/parser/parser.go

@@ -55,7 +55,7 @@ func init() {
 		"cmd":            parseMaybeJSON,
 		"entrypoint":     parseMaybeJSON,
 		"expose":         parseStringsWhitespaceDelimited,
-		"volume":         parseMaybeJSON,
+		"volume":         parseMaybeJSONToList,
 		"insert":         parseIgnore,
 	}
 }