error shows when try to install

[adamhk0]

I have a clean ubuntu 14.04 set up.

root@:~# wget http://sentora.org/install
--2015-03-28 12:41:32-- http://sentora.org/install
Resolving sentora.org (sentora.org)... 5.196.10.149
Connecting to sentora.org (sentora.org)|5.196.10.149|:80... connected.
HTTP request sent, awaiting response... 302 Found
Location: https://raw.githubusercontent.com/sentor...install.sh [following]
--2015-03-28 12:41:33-- https://raw.githubusercontent.com/sentor...install.sh
Resolving raw.githubusercontent.com (raw.githubusercontent.com)... 199.27.74.133
Connecting to raw.githubusercontent.com (raw.githubusercontent.com)|199.27.74.133|:443... connected.
ERROR: cannot verify raw.githubusercontent.com's certificate, issued by '/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert SHA2 High Assurance Server CA':
Unable to locally verify the issuer's authority.
To connect to raw.githubusercontent.com insecurely, use `--no-check-certificate'.

I wonder if it is normal? or something wrong in the server site?
Should I execute with --no-check-certificate