update redis cheatsheet

HLEN had the same description as HKEYS. Fixed it to say that it gets the number of fields instead of the fields themselves.

databases/redis.sh

@@ -115,7 +115,7 @@ HINCRBY key field increment  # increment value in hash by X
 HDEL key field [field ...]   # delete one or more hash fields
 HEXISTS key field            # determine if a hash field exists
 HKEYS key                    # get all the fields in a hash
-HLEN key                     # get all the fields in a hash
+HLEN key                     # get the number of fields in a hash
 HSTRLEN key field            # get the length of the value of a hash field
 HVALS key                    # get all the values in a hash