cmd/nvim-go: change get debug and pprof env to use var and len
cmd/nvim-go: change get debug and pprof env to use var and len

Signed-off-by: Koichi Shiraishi <2e5bdfebde234ed3509bcfc18121c70b6631e207@gmail.com>

zchee/nvim-go,zchee/nvim-go