add Travis-CI support

pkgs/stack_trace/.travis.yml

diff --git a/pkgs/stack_trace/.travis.yml b/pkgs/stack_trace/.travis.yml
new file mode 100644
index 0000000..b6198f7
--- /dev/null
+++ b/pkgs/stack_trace/.travis.yml
@@ -0,0 +1,24 @@
+language: dart
+sudo: false
+dart:
+  - stable
+  - dev
+  - 1.22.1
+  - 1.21.1
+  - 1.20.1
+  - 1.19.1
+dart_task:
+  - test: -p vm
+  - test: -p firefox
+  - test: -p dartium
+    install_dartium: true
+  - dartanalyzer
+matrix:
+  include:
+    # Only validate formatting using the dev release
+    # Formatted with 1.23.0+ which has (good) changes since 1.22.1
+    - dart: dev
+      dart_task: dartfmt
+cache:
+  directories:
+    - $HOME/.pub-cache