corrected typo

slides/cours_13.md

@@ -137,7 +137,7 @@ bool binary_get1(int n, value_key_t table[n], key_t key, value_t *value) {
     int top = n - 1, bottom = 0;
     while (top > bottom) { 
         int middle = (top + bottom) / 2;
-        if (x > table[middle]) {
+        if (key > table[middle].key) {
             bottom  = middle+1;
         } else {
             top = middle;