Travis build without sudo

.travis.yml

@@ -1,21 +1,34 @@
 language: rust
-sudo: required
 
 rust:
   - stable
   - beta
   - nightly
+
+sudo: false
+
+cache:
+    apt: true
+    directories:
+        - target/debug/deps
+        - target/debug/build
+
+install: pip install 'travis-cargo<0.2' --user && export PATH=$HOME/.local/bin:$PATH
+
+addons:
+  apt:
+    packages:
+      - postfix
+
 before_script:
-  - sudo apt-get update -qq
-  - sudo apt-get install -y postfix
-  - pip install 'travis-cargo<0.2' --user && export PATH=$HOME/.local/bin:$PATH
   - smtp-sink 2525 1000&
+
 script:
-  - |
-      travis-cargo build &&
-      travis-cargo test &&
-      travis-cargo doc
+  - travis-cargo build
+  - travis-cargo test
+  - travis-cargo doc
   - 'if [ $TRAVIS_RUST_VERSION = nightly ]; then cargo bench; fi'
+
 after_success:
   - travis-cargo --only stable doc-upload
   - travis-cargo --only stable coveralls