add bors

.github/bors.toml

@@ -0,0 +1,5 @@
+block_labels = ["S-blocked"]
+delete_merged_branches = true
+status = [
+  "continuous-integration/travis-ci/push",
+]

.travis.yml

@@ -9,6 +9,12 @@ matrix:
     - rust: nightly
       env: FEATURES='bkpt'
 
+branches:
+  only:
+    - staging
+    - trying
+    - master
+
 before_script:
   - rustup target add thumbv7em-none-eabihf
     # - rustup component add clippy