Re-enable -Wshorten-64-to-32 compilation flag.

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index b3753ed..ea42cc8 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -143,7 +143,7 @@
   ei_add_cxx_compiler_flag("-Wpointer-arith")
   ei_add_cxx_compiler_flag("-Wwrite-strings")
   ei_add_cxx_compiler_flag("-Wformat-security")
-#   ei_add_cxx_compiler_flag("-Wshorten-64-to-32")
+  ei_add_cxx_compiler_flag("-Wshorten-64-to-32")
   ei_add_cxx_compiler_flag("-Wenum-conversion")
   ei_add_cxx_compiler_flag("-Wc++11-extensions")