Find the right version of Lua.

Index: CMakeLists.txt
--- CMakeLists.txt.orig
+++ CMakeLists.txt
@@ -342,7 +342,7 @@ SET(TeXworks_LIBS
 # -------------------------------
 
 IF ( WITH_LUA )
-  FIND_PACKAGE(Lua)
+  FIND_PACKAGE(Lua "${MODLUA_VERSION}" EXACT REQUIRED)
 ENDIF()
 
 IF ( WITH_PYTHON )
