Merge pull request #1570 from PaddlePaddle/gangliao-patch-2

Set Protobuf 3.1 in FIND_PACKAGE

Author: gangliao

cmake/external/protobuf.cmake

@@ -14,7 +14,7 @@
 
 INCLUDE(ExternalProject)
 
-FIND_PACKAGE(Protobuf)
+FIND_PACKAGE(Protobuf 3.1)
 
 IF(NOT PROTOBUF_FOUND)
     SET(PROTOBUF_SOURCES_DIR ${THIRD_PARTY_PATH}/protobuf)