Bump travis 2.12 version to 2.12.3

[suhasgaddam]

github4s is pulling the crossScalaVersions from sbt-org-policies. It has 2.12 has 2.12.3 which is different than travis's 2.12.2. The release task has a filter that only allows it to run for the latest crossScalaVersion.

Reference links in some order:
https://github.com/47deg/sbt-org-policies/blob/v0.7.5/core/src/main/scala/sbtorgpolicies/model.scala#L138

https://github.com/47deg/github4s/blob/master/project/ProjectPlugin.scala#L94

https://travis-ci.org/47deg/github4s/jobs/279420156#L2119
https://travis-ci.org/47deg/github4s/jobs/279420156#L2121

[BenFradet]

Nice! 👍

[juanpedromoreno]

Good catch, thanks @suhasgaddam !

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@7282077). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #166   +/-   ##
=========================================
  Coverage          ?   87.11%           
=========================================
  Files             ?       42           
  Lines             ?      621           
  Branches          ?        5           
=========================================
  Hits              ?      541           
  Misses            ?       80           
  Partials          ?        0

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7282077...fe7bd45. Read the comment docs.