Fix use of deprecated failure_message_should

- Replaced with failure_message
Merge pull request #3043 from prathamesh-sonpatki/fix-deprecation-warning-for-failure-message-should

Fix use of deprecated failure_message_should

[ci skip]
Extract standalone path expansion to do it only once
Merge pull request #3044 from Juanxo/extract-standalone-path-expansion

Extract standalone path expansion to do it only once
fix the rspec rake task on 1.8.7
check rspec version while running specs
add travis results to slack #general room

[ci skip]