Fix typo, noted by Wolfgang Glunz.

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 9f28287..79a73bb 100755
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -75,7 +75,7 @@
 ENDIF(ZLIB_VERSION_STRING VERSION_LESS "1.1.2")
 
 IF(MSVC)
-ADD_DEFINITIONS("-D_CRT_SECURE_NO_WARNING")
+ADD_DEFINITIONS("-D_CRT_SECURE_NO_WARNINGS")
 ENDIF(MSVC)
 
 # Targets