aborted(core dump) issue 

Hi experts, I met the following issue when running tutorial01/solutions/vector_add.cu:
```
[heyliu@controller tutorial01]$ ./vector_add
vector_add: vector_add.cu:48: int main(): Assertion `fabs(output[i] - a[i] - b[i]) < 1e-6' failed.
Aborted (core dumped)
```

any idea here, thanks!
