Stop testing on Dartium (dart-lang/stack_trace#39)

pkgs/stack_trace/.travis.yml

diff --git a/pkgs/stack_trace/.travis.yml b/pkgs/stack_trace/.travis.yml
index 2ec03bb..1d12365 100644
--- a/pkgs/stack_trace/.travis.yml
+++ b/pkgs/stack_trace/.travis.yml
@@ -7,8 +7,6 @@
 dart_task:
   - test: -p vm
   - test: -p firefox
-  - test: -p dartium
-    install_dartium: true
   - dartanalyzer
 matrix:
   include: