Parse untyped object type members separated by ','

Previously if the first member was untyped and the separator was ',',
then parsing would fail.

src/compiler/parser.ts

@@ -2339,6 +2339,7 @@ namespace ts {
                     token() === SyntaxKind.LessThanToken ||
                     token() === SyntaxKind.QuestionToken ||
                     token() === SyntaxKind.ColonToken ||
+                    token() === SyntaxKind.CommaToken ||
                     canParseSemicolon();
             }
             return false;