TST: vector_n: Fixed conversion warning

```
boost\fusion\container\vector\vector.hpp(168): warning C4244: 'initializing': conversion from 'T' to 'T', possible loss of data
1>        with
1>        [
1>            T=int
1>        ]
1>        and
1>        [
1>            T=float
1>        ]
```

test/sequence/vector_n.cpp

@@ -94,7 +94,7 @@ main()
     }
 
     {
-        vector2<int, int> t1(123, 456);
+        vector2<int, short> t1(123, 456);
         vector2<double, float> t2(t1);
         (void)t2;
     }