PEP fix styling around docstring

[priyanshuone6]

I found these styling errors around docstring in functions in various files that doesn't adhere to Python's PEP guidelines.

PyBaMM/pybamm/citations.py

Lines 29 to 30 in 9883106

	def _reset(self):
	"Reset citations to default only (only for testing purposes)"

PyBaMM/pybamm/settings.py

Lines 32 to 33 in 9883106

	def set_smoothing_parameters(self, k):
	"Helper function to set all smoothing parameters"

PyBaMM/pybamm/util.py

Lines 63 to 64 in 9883106

	def get_best_matches(self, key):
	"Get best matches from keys"

Expected behavior
Find all those functions and replace " with 3 double quotes """ for consistency across the repository .

It can be marked as a good first issue

[asinghgaba]

If anyone’s not working on it, I can get this done.

[valentinsulzer]

There are probably several other places where it's like this, I wasn't aware of the PEP guideline for this