Travis: fix a typo

.travis.yml

@@ -100,7 +100,7 @@ addons:
 #osx_image: xcode9.4
 
 before_install:
-  ## If we're on OSX, homebrew usually needs to updated first
+  ## If we're on OSX, homebrew usually needs to be updated first
   - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then brew update; fi
   ## We might be upgrading some useless packages, but that's better than missing an upgrade
   - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then brew upgrade; fi