Download (Zip File)
Exract it and copy this file in your RailsInstaller folder (C:\RailsInstaller\cacert.pem) as a .pem file.
Go to your Computer -> Advanced Settings -> Environment Variables
Create a new System Variable:
Variable: SSL_CERT_FILE Value: C:\RailsInstaller\cacert.pem
Close all your command prompts, including your Rails server command prompt, etc.
Note: First close all the command prompts and try all commands.