Add ruby25 to TravisCI testing

[blkperl]

Goal

Testing bugsnag against Ruby 2.5

Changeset

Tests

Discussion

Alternative Approaches

Outstanding Questions

Linked issues

Review

For the submitter, initial self-review:

• Commented on code changes inline explain the reasoning behind the approach
• Reviewed the test cases added for completeness and possible points for discussion
• A changelog entry was added for the goal of this pull request
• Check the scope of the changeset - is everything in the diff required for the pull request?
• This pull request is ready for:
  • Initial review of the intended approach, not yet feature complete
  • Structural review of the classes, functions, and properties modified
  • Final review

For the pull request reviewer(s), this changeset has been reviewed for:

• Consistency across platforms for structures or concepts added or modified
• Consistency between the changeset and the goal stated above
• Internal consistency with the rest of the library - is there any overlap between existing interfaces and any which have been added?
• Usage friction - is the proposed change in usage cumbersome or complicated?
• Performance and complexity - are there any cases of unexpected O(n^3) when iterating, recursing, flat mapping, etc?
• Concurrency concerns - if components are accessed asynchronously, what issues will arise
• Thoroughness of added tests and any missing edge cases
• Idiomatic use of the language

[Cawllec]

Hi @blkperl, thanks, this looks good to me. I'm just going to check where our current linting/coverage tools should be, then will get it merged.

[Cawllec]

Hi @blkperl, I've made some adjustments and created a new PR here. We'll get that merged with your contribution ASAP. Thanks!