Whitelist 4 new TextMate grammar fields (#4039)

swallow, foregroundColor, and backgroundColor are older fields for TextMate 1.

tools/grammars/compiler/data.go

@@ -28,4 +28,8 @@ var KnownFields = map[string]bool{
 	"limitLineLength":       true,
 	"hideFromUser":          true,
 	"injectionSelector":     true,
+	"swallow":               true,
+	"foregroundColor":       true,
+	"backgroundColor":       true,
+	"increaseIndentPattern": true,
 }