reformat options to avoid errors with custom models

[valentinsulzer]

Description

Type of change

Please add a line in the relevant section of CHANGELOG.md to document the change (include PR #) - note reverse order of PR #s. If necessary, also add to the list of breaking changes.

• New feature (non-breaking change which adds functionality)
• Optimization (back-end change that speeds up the code)
• Bug fix (non-breaking change which fixes an issue)

Key checklist:

• No style issues: $ flake8
• All tests pass: $ python run-tests.py --unit
• The documentation builds: $ cd docs and then $ make clean; make html

You can run all three at once, using $ python run-tests.py --quick.

Further checks:

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[codecov]

Codecov Report

Base: 99.67% // Head: 99.69% // Increases project coverage by +0.02% 🎉

Coverage data is based on head (422296c) compared to base (e090ada).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2571      +/-   ##
===========================================
+ Coverage    99.67%   99.69%   +0.02%     
===========================================
  Files          271      271              
  Lines        19558    19540      -18     
===========================================
- Hits         19494    19480      -14     
+ Misses          64       60       -4     

Impacted Files	Coverage Δ
...ybamm/models/full_battery_models/lead_acid/full.py	100.00% <ø> (ø)
...ybamm/models/full_battery_models/lead_acid/loqs.py	100.00% <ø> (ø)
...bamm/models/full_battery_models/lithium_ion/dfn.py	100.00% <ø> (ø)
...bamm/models/full_battery_models/lithium_ion/mpm.py	100.00% <ø> (ø)
...s/full_battery_models/lithium_ion/newman_tobias.py	100.00% <ø> (ø)
...bamm/models/full_battery_models/lithium_ion/spm.py	100.00% <ø> (ø)
...amm/models/full_battery_models/lithium_ion/spme.py	100.00% <ø> (ø)
pybamm/geometry/battery_geometry.py	100.00% <100.00%> (ø)
...m/models/full_battery_models/base_battery_model.py	99.78% <100.00%> (-0.01%)	⬇️
...full_battery_models/equivalent_circuit/thevenin.py	100.00% <100.00%> (ø)
... and 5 more

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[brosaplanella]

Looks good, thanks!