minor fix of road map - update link (#2788)

ROADMAP_2019.md

@@ -1,4 +1,4 @@
-This roadmap is produced based on Cats ecosystem community survey 2018 results - See [#2719](https://github.com/typelevel/cats/issues/2719)
+This roadmap is produced based on [Cats ecosystem community survey 2018 results](https://typelevel.org/blog/2019/01/30/cats-ecosystem-community-survey-results.html).
 
 ## Overall strategy
 A Cats 2.0 is released earlier in the year **without any breaking changes on most modules** except `cats-laws` and `cats-testkit`. We then start branching to allow the master branch to drop Scala 2.11 in Q2, but maintain a dedicated `scala2_11` branch to continue support Scala 2.11 until near the end of 2019. During this period, we are going to backport incoming changes from `master` to the `scala2_11` branch in a Scala 2.11 BC way. We will try to maintain as much as possible use site source compatibility between on Scala 2.11 code and Scala 2.12+ - but they will be source incompatible - mostly methods added to traits in 2.12 will only be available in 2.11 code in new `XXXXBinCompatN` traits. During this period, we'll release Cats on scala 2.12+ and 2.11 from two different branches.