=> Bootstrap dependency digest>=20010302: found digest-20160304
=> Fetching graphopt-0.4.1.tgz
=> Total size: 77612 bytes
Certificate verification failed for /C=US/O=Let's Encrypt/CN=Let's Encrypt Authority X3
34374371912:error:14090086:SSL routines:ssl3_get_server_certificate:certificate verify failed:/usr/src/crypto/openssl/ssl/s3_clnt.c:1269:
fetch: http://downloads.sourceforge.net/sourceforge/graphopt/graphopt-0.4.1.tgz: Authentication error
fetch: Unable to fetch expected file graphopt-0.4.1.tgz
graphopt-0.4.1.tgz                                       0  B    0  Bps
=> Checksum SHA1 OK for graphopt-0.4.1.tgz
=> Checksum RMD160 OK for graphopt-0.4.1.tgz
=> Checksum SHA512 OK for graphopt-0.4.1.tgz