Using protobuf3 in Travis-CI MacOS.

paddle/scripts/travis/before_install.osx.sh

@@ -2,9 +2,8 @@
 brew update
 brew tap homebrew/science
 brew install python
-sudo pip install --upgrade protobuf==2.6.0
-brew install homebrew/versions/protobuf260 --without-python
-brew install cmake python glog gflags openblas wget md5sha1sum
+sudo pip install --upgrade protobuf
+brew install cmake python glog gflags openblas wget md5sha1sum protobuf
 
 wget https://github.com/google/googletest/archive/release-1.8.0.tar.gz -O gtest.tar.gz
 tar xf gtest.tar.gz