Fix wording in Classes.md on name private member
Fix wording in Classes.md on name private member

This change fixes a grammatical error introduced in this commit: https://github.com/Microsoft/TypeScript-Handbook/commit/76cb268c82ef6c4474c80c74930ba744060259c0

The fix was made working from the assumption that the referenced commit intended to further shorten the wording in the changed sentence (like changing "it is" to "it's").
gooddaytoday/TypeScript-Handbook-RU,Microsoft/TypeScript-Handbook,drmacm/TypeScript-Handbook,zspitz/TypeScript-Handbook,mahp/TypeScript-Handbook