docs: fixed typos where "redis" should have been "mysql". thanks doledoletree for reporting it.

Author: agentzh

README.markdown

@@ -168,13 +168,13 @@ set_keepalive
 ------------
 `syntax: ok, err = db:set_keepalive(max_idle_timeout, pool_size)`
 
-Puts the current Redis connection immediately into the ngx_lua cosocket connection pool.
+Puts the current MySQL connection immediately into the ngx_lua cosocket connection pool.
 
 You can specify the max idle timeout (in ms) when the connection is in the pool and the maximal size of the pool every nginx worker process.
 
 In case of success, returns `1`. In case of errors, returns `nil` with a string describing the error.
 
-Only call this method in the place you would have called the `close` method instead. Calling this method will immediately turn the current redis object into the `closed` state. Any subsequent operations other than `connect()` on the current objet will return the `closed` error.
+Only call this method in the place you would have called the `close` method instead. Calling this method will immediately turn the current `resty.mysql` object into the `closed` state. Any subsequent operations other than `connect()` on the current objet will return the `closed` error.
 
 get_reused_times
 ----------------