Fixed CMake build issue when building with Clang. (#4465)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index e9ba528..a4cccae 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -131,8 +131,7 @@
 
 elseif(${CMAKE_CXX_COMPILER_ID} MATCHES "Clang")
   set(CMAKE_CXX_FLAGS
-      "${CMAKE_CXX_FLAGS} -std=c++0x -Wall -pedantic -Werror \
-                          -Wextra -Wno-unused-parameter")
+      "${CMAKE_CXX_FLAGS} -std=c++0x -Wall -pedantic -Werror -Wextra -Wno-unused-parameter")
   if(NOT "${CMAKE_SYSTEM_NAME}" MATCHES "Linux")
     set(CMAKE_CXX_FLAGS
         "${CMAKE_CXX_FLAGS} -stdlib=libc++")