The build was failing on check-requirements because of an issue with cygwin.com certificate. I changed URL in requirements.json from https to http. It should be changed back to https as soon as possible.
How to reproduce:
$ wget https://cygwin.com/setup-x86_64.exe --2016-04-13 09:14:28-- https://cygwin.com/setup-x86_64.exe Resolving cygwin.com (cygwin.com)... 209.132.180.131 Connecting to cygwin.com (cygwin.com)|209.132.180.131|:443... connected. ERROR: cannot verify cygwin.com's certificate, issued by ‘CN=DigiCert SHA2 High Assurance Server CA,OU=www.digicert.com,O=DigiCert Inc,C=US’: Unable to locally verify the issuer's authority. To connect to cygwin.com insecurely, use `--no-check-certificate'.