Update Rails: 4.1.7 and sprockets

Current version (4.1.5) contains several security issues:

```
ruby-advisory-db: 102 advisories
Name: actionpack
Version: 4.1.5
Advisory: CVE-2014-7818
Criticality: Unknown
URL: https://groups.google.com/forum/#!topic/rubyonrails-security/dCp7duBiQgo
Title: Arbitrary file existence disclosure in Action Pack
Solution: upgrade to ~> 3.2.20, ~> 4.0.11, ~> 4.1.7, >= 4.2.0.beta3

Name: sprockets
Version: 2.11.0
Advisory: CVE-2014-7819
Criticality: Unknown
URL: https://groups.google.com/forum/#!topic/rubyonrails-security/doAVp0YaTqY
Title: Arbitrary file existence disclosure in Sprockets
Solution: upgrade to ~> 2.0.5, ~> 2.1.4, ~> 2.2.3, ~> 2.3.3, ~> 2.4.6, ~> 2.5.1, ~> 2.7.1, ~> 2.8.3, ~> 2.9.4, ~> 2.10.2, ~> 2.11.3, ~> 2.12.3, >= 3.0.0.beta.3
```