fixed Woverflow warning

snf_saccades.hpp

   private:
     const static unsigned int stretchSize = 8;
     const static unsigned int stretchMark = stretchSize / 2;
-    const static unsigned int stretchMask = ((~0UL) ^ (stretchSize - 1));
+    const static unsigned int stretchMask = ((~0U) ^ (stretchSize - 1));
 
     unsigned int stretchLeft(unsigned int s) {
         s = (stretchMark > s) ? s : (s - (stretchMark));