LGTM.com - false positive when using imports with TYPE_CHECKING

**Description of the false positive**

lgtm complains that a "Module is imported more than once" in my python code, but the first import ist protected by "if TYPE_CHECKING:", which is required for mypy type checking to work properly. I think lgtm should simply ignore imports that are under `TYPE_CHECKING`.

**URL to the alert on the project page on LGTM.com**

Here is the concrete error:
https://lgtm.com/projects/g/zwicker-group/py-pde/snapshot/67363039e04aebcfba93b01fcf65014bec37aebb/files/pde/tools/plotting.py?sort=name&dir=ASC&mode=heatmap#x70f271ca0359e14c:1