fix: typo in Float64 documentation (#515)

Correct a cut and past error in the Float64 documentation which listed the return type as int instead of float64
diff --git a/redis/reply.go b/redis/reply.go
index 251a788..f32368f 100644
--- a/redis/reply.go
+++ b/redis/reply.go
@@ -118,7 +118,7 @@
 // Float64 is a helper that converts a command reply to 64 bit float. If err is
 // not equal to nil, then Float64 returns 0, err. Otherwise, Float64 converts
-// the reply to an int as follows:
+// the reply to a float64 as follows:
 //  Reply type    Result
 //  bulk string   parsed reply, nil