[go] Fix no new variables on left side of :=

Cannot short declaration twice without at least one new var.  Also changing type from string to slice.

$ go run learnxiny.go
# command-line-arguments
./learnxiny.go:83: no new variables on left side of :=
./learnxiny.go:83: cannot use []int literal (type []int) as type string in assignment
./learnxiny.go:84: first argument to append must be slice; have string
./learnxiny.go:90: first argument to append must be slice; have string