allow_failures needs to be in a matrix:

dalehenrich · dalehenrich · commit a8b603fb03b1 · 2016-08-26T15:05:24.000+02:00
diff --git a/.travis.yml b/.travis.yml
@@ -15,5 +15,6 @@ smalltalk:
 cache:
   directories:
     - $SMALLTALK_CI_CACHE
-allow_failures:
-  - smalltalk: Pharo-6.0
+matrix:
+  allow_failures:
+    - smalltalk: Pharo-6.0
