Rename PrivateName.name to .id (#698)

Given that it refers to an identifier, it's somewhat confusing to have
to use .name.name to get the actual string. The type declared within
types.js is also incorrect, which this commit fixes.

src/parser/expression.js

@@ -815,7 +815,7 @@ export default class ExpressionParser extends LValParser {
 
     if (isPrivate) {
       const node = this.startNode();
-      node.name = this.parseIdentifier(true);
+      node.id = this.parseIdentifier(true);
       return this.finishNode(node, "PrivateName");
     } else {
       return this.parseIdentifier(true);