=> Bootstrap dependency digest>=20010302: found digest-20160304
=> Fetching pngquant-2.12.0-src.tar.gz
=> Total size: 143335 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://pngquant.org/pngquant-2.12.0-src.tar.gz: Authentication error
fetch: Unable to fetch expected file pngquant-2.12.0-src.tar.gz
pngquant-2.12.0-src.tar.gz                               0  B    0  Bps
=> Checksum SHA1 OK for pngquant-2.12.0-src.tar.gz
=> Checksum RMD160 OK for pngquant-2.12.0-src.tar.gz
=> Checksum SHA512 OK for pngquant-2.12.0-src.tar.gz