#1077 update quickplot for fem

[rtimms]

Description

Fixes plots of variables discretised using FEM (y,z) in quickplot

Fixes #1077

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

[brosaplanella]

Looks good, thanks Rob!

[codecov]

Codecov Report

Merging #1078 into develop will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop    #1078   +/-   ##
========================================
  Coverage    97.74%   97.74%           
========================================
  Files          242      242           
  Lines        12528    12532    +4     
========================================
+ Hits         12245    12249    +4     
  Misses         283      283           

Impacted Files	Coverage Δ
pybamm/plotting/quick_plot.py	100.00% <100.00%> (ø)

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