fix MySQL spell (#549)

as MySQl to MySQL

Author: igoso

client/auth.go

@@ -106,7 +106,7 @@ func (c *Conn) readInitialHandshake() error {
 // generate auth response data according to auth plugin
 //
 // NOTE: the returned boolean value indicates whether to add a \NUL to the end of data.
-//       it is quite tricky because MySQl server expects different formats of responses in different auth situations.
+//       it is quite tricky because MySQL server expects different formats of responses in different auth situations.
 //       here the \NUL needs to be added when sending back the empty password or cleartext password in 'sha256_password'
 //       authentication.
 func (c *Conn) genAuthResponse(authData []byte) ([]byte, bool, error) {