CacheGetManyConcurrent tests has incorrect key

[Gobd]

I think these two lines should be k := "foo" + strconv.Itoa(i) (i instead of n) so that each key is different. This will make the sharded cache look better since keys will be able to spread out.

• https://github.com/patrickmn/go-cache/blob/master/sharded_test.go#L68
• https://github.com/patrickmn/go-cache/blob/master/cache_test.go#L1558

[patrickmn]

Yep, you're right. What a weird mistake -- thanks for noticing it. Will fix shortly.