travis: one-line for the brew install (minor)

Author: paulirish

.travis.yml

@@ -1,8 +1,8 @@
 language: bash
 before_install:
   - git clone --depth 1 https://github.com/sstephenson/bats.git
-  - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then brew update         ; fi
-  - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then brew install gnu-sed; fi
+  - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then brew update; brew install gnu-sed; fi
+
 script:
   - ./bats/bin/bats test/*.bats
 os: