last success was https://travis-ci.org/scala/scala/builds/65345691, first failure was https://travis-ci.org/scala/scala/builds/65747400 . Adriaan diffed the logs and noted:

-Installing redcarpet 3.2.3
+Installing redcarpet 3.3.0

fwiw, varying the Ruby version between 1.9.3, 2.0, 2.2.0, and 2.2.2 did not help.

the cause might have been vmg/redcarpet#494, or perhaps the similarity is coincidental