Fix a misspelling in MySQL types document
//! | Rust type | MySQL type(s) |
//! |---------------------------------------|------------------------------------------------------|
//! | `chrono::DateTime<Utc>` | TIMESTAMP |
-//! | `chrono::DateTime<Local>` | TIMETAMP |
+//! | `chrono::DateTime<Local>` | TIMESTAMP |
//! | `chrono::NaiveDateTime` | DATETIME |
//! | `chrono::NaiveDate` | DATE |
//! | `chrono::NaiveTime` | TIME |
