Fix typo in 2857-roadmap-2020.md

Author: teor2345

text/2857-roadmap-2020.md

@@ -127,7 +127,7 @@ people transition their code, though the tooling might not be
 completed this year.
 
 It is notable also that the 2018 edition packaged two "experiences" into one:
-breaking changes and a reflection for the world on the work in past 3 years.
+breaking changes and a reflection for the world on the work in the past 3 years.
 That did not go as perfectly as we had hoped, and to this day there remains some
 confusion on this point. We should, by 2021, identify the marketing strategy we
 will use for the edition, but this should not affect the choices of breaking