Add signature for codeship.aes

[dcepler]

gitrob does not detect codeship.aes files. codeship.aes contains projects-specific AES keys to encrypt/decrypt environment variables used in Codeship Pro. It should be added to .gitignore but might be missed.

https://documentation.codeship.com/pro/builds-and-configuration/environment-variables/#encrypted-environment-variables

Expected Behavior

gitrob flag codeship.aes files.

Actual Behavior

gitrob does not flag codeship.aes files.

Steps to Reproduce the Problem

1. Add codeship.aes to public github repository for an organization (use junk text for contents not real file)
2. Execute gitrob on organization

Specifications

• Gitrob version: 2.0.0-beta
• Operating system: macOS 10.13.6
• Go version: 1.11

[mattyjones]

@dcepler This has been merged into the new fork