Install protobuf3 to /usr

paddle/scripts/travis/before_install.linux.sh

@@ -6,7 +6,7 @@ wget https://github.com/google/protobuf/archive/v3.0.2.tar.gz -O protobuf.tar.gz
 tar xf protobuf.tar.gz
 cd protobuf*
 ./autogen.sh
-./configure
+./configure --prefix=/usr/
 make -j 2 install
 cd ..
 rm -rf protobuf*

paddle/scripts/travis/main.sh

 #!/bin/bash
 cd `dirname $0`
 
-if [ "$TRAVIS_OS_NAME" == "linux" ]; then
-  # for manually installed protobuf 3.10
-  export LD_LIBRARY_PATH=/usr/local/lib/:$LD_LIBRARY_PATH
-fi
-
 if [ ${JOB} == "BUILD_AND_TEST" ]; then
   ./build_and_test.sh
 elif [ ${JOB} == "DOCS" ]; then