migrate from `dartfmt` to `dart format`

pkgs/stack_trace/.travis.yml

diff --git a/pkgs/stack_trace/.travis.yml b/pkgs/stack_trace/.travis.yml
index 6d6ea7c..e87b827 100644
--- a/pkgs/stack_trace/.travis.yml
+++ b/pkgs/stack_trace/.travis.yml
@@ -12,7 +12,7 @@
     - stage: analyze_and_format
       name: "Format"
       os: linux
-      script: dartfmt -n --set-exit-if-changed .
+      script: dart format -o none --set-exit-if-changed .
     - stage: test
       name: "Vm Tests"
       os: linux