ci(travis): keep macOS Homebrew boost/cmake without OpenCV

Differentiates from PR Syncleus#219: still updates brew deps on osx while
skipping the failing opencv install that disabled the matrix entry.

Author: isaaclins

.travis.yml

@@ -238,8 +238,10 @@ before_install:
         #sudo apt-get install -qq -y clang-3.7 libclang-common-3.7-dev libclang-3.7-dev libclang1-3.7 libllvm3.7 lldb-3.7 llvm-3.7 llvm-3.7-dev llvm-3.7-runtime clang-modernize-3.7 clang-format-3.7 lldb-3.7-dev
       # OSX
       elif [[ ${TRAVIS_OS_NAME} == "osx" ]]; then
-        # macOS job runs Maven/Java; skip Homebrew OpenCV that broke this matrix entry.
-        true
+        # Keep lightweight Homebrew deps; skip OpenCV (exit 1) that disabled this job.
+        brew update
+        brew outdated boost || brew upgrade boost
+        brew outdated cmake || brew upgrade cmake
       fi
     - gem install coveralls-lcov
     - if [ "$CXX" = "g++" ]; then export CXX="g++-4.8" CC="gcc-4.8"; fi