fix(core) bootstrap panic

@jbenet @mappum

License: MIT
Signed-off-by: Brian Tiger Chow <brian@perfmode.com>
Merge pull request #425 from jbenet/fix/bootstrap-panic

fix(core) bootstrap panic
fix dep

License: MIT
Signed-off-by: Brian Tiger Chow <brian@perfmode.com>
feat(core) dht.Bootstrap

License: MIT
Signed-off-by: Brian Tiger Chow <brian@perfmode.com>