corrected typo

exemples/opaque/main.c

@@ -8,4 +8,4 @@ int main()
     set(t, 10);
     printf("%d\n", get(t));
     destroy(&t);
-}
\ No newline at end of file
+}

slides/opaque.md

@@ -130,7 +130,7 @@ tab.data[9] = 10;
 
     ```C
     int main() {
-        struct table *t = create();
+        table t;
         init(&t);
         set_a(t, 10);
         printf("%d\n", get_a(t));