hash/maphash: typo in the documentation of Hash

[fluhus]

The word Seed appears twice, want once.

go/src/hash/maphash/maphash.go

Line 37 in 66c2709

// the first call to a Reset, Write, Seed, Sum64, or Seed method.

https://golang.org/pkg/hash/maphash/#Hash

[gopherbot]

Change https://golang.org/cl/291631 mentions this issue: hash/maphash: remove duplicate from Hash documentation