Typo in gauss_1d_analysis.py?

Hi there, 

There seems to be a typo on line 77 of `gauss_1d_analysis.py`: the line should be broken down to 
```
x_axis = [i for i in np.linspace(-3, 3, 512)]
x_axis.append(0.)
```
Otherwise it will complain about None Type since `append()` returns None. Thanks!