[rs] Merge #128

128: Small updates r=kvark a=Coder-256

Enable Travis CI cache, disable [deprecated container-based builds](https://docs.travis-ci.com/user/reference/trusty/#container-based-infrastructure), and add `red.png` to `.gitignore` (output from `cargo run --example capture`).

Co-authored-by: Jacob Greenfield <jacob@jacobgreenfield.me>

.gitignore

@@ -11,3 +11,6 @@ Cargo.lock
 
 # Other
 .DS_Store
+
+# Output from capture example
+red.png

.travis.yml

@@ -1,5 +1,5 @@
 language: rust
-sudo: false
+cache: cargo
 os:
   - linux
   - osx