BUG: documentation example

# Description
There's a typo in the docs

# To Reproduce this bug:
Steps to reproduce the behavior:
1. Go to: https://pyintensityfeatures.readthedocs.io/en/latest/examples/ex_fitting.html#find-the-boundaries-for-different-gaussian-fits
2. See: "from pyIntensityFeatures.utils import distribution"
3. Should be: "from pyIntensityFeatures.utils import distributions"