docs: fix README typo (#1068)

README.md

@@ -759,7 +759,7 @@ ioredis **guarantees** that the node you connected to is always a master even af
 
 It's possible to connect to a slave instead of a master by specifying the option `role` with the value of `slave` and ioredis will try to connect to a random slave of the specified master, with the guarantee that the connected node is always a slave. If the current node is promoted to master due to a failover, ioredis will disconnect from it and ask the sentinels for another slave node to connect to.
 
-If you specify the option `preferredSlaves` along with `role: 'slave'` ioredis will attempt to use this value when selecting the slave from the pool of available slaves. The value of `preferredSlaves` should either be a function that accepts an array of avaiable slaves and returns a single result, or an array of slave values priorities by the lowest `prio` value first with a default value of `1`.
+If you specify the option `preferredSlaves` along with `role: 'slave'` ioredis will attempt to use this value when selecting the slave from the pool of available slaves. The value of `preferredSlaves` should either be a function that accepts an array of available slaves and returns a single result, or an array of slave values priorities by the lowest `prio` value first with a default value of `1`.
 
 ```javascript
 // available slaves format