It looks like the cached path
- `$GOPATH/src`
- `$GOPATH/pkg`
overlaps with the source path of
`$GOPATH/src/github.com/coredns/coredns`.

Disable the cache for now.

May enable cache in the future if we could exclude
`$GOPATH/src/github.com/coredns/coredns` from `$GOPATH/src`.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>