Integral Transform error #8400

I am a newbie in the world of open source and would love to work with sympy.

I edited the code as was given on the issue page.
Thank You.

```
In [7]: i.transform(x, (y + 2*z, y)).doit()
Out[7]: 
                                             2             2
-2⋅z⋅(-2⋅z + 1) + 2⋅z⋅(-2⋅z + 2) - (-2⋅z + 1)  + (-2⋅z + 2) 
```