make sure citations file closed after read

[chuckliu1979]

Description

citations file not closed in pybamm.citations.Citations.read_citations which causes pytest failed if import pybamm:

_pytest/unraisableexception.py:78: in unraisable_exception_runtest_hook
warnings.warn(pytest.PytestUnraisableExceptionWarning(msg))
E pytest.PytestUnraisableExceptionWarning: Exception ignored in: <_io.FileIO [closed]>
E
E Traceback (most recent call last):
E File "pybamm/citations.py", line 45, in read_citations
E for line in open(citations_file):
E ResourceWarning: unclosed file <_io.TextIOWrapper name='pybamm/CITATIONS.txt' mode='r' encoding='UTF-8'>

Fixes # (issue)

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

Merging #1620 (1696630) into develop (b12c3ee) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 1696630 differs from pull request most recent head 1e617db. Consider uploading reports for the commit 1e617db to get more accurate results

@@             Coverage Diff             @@
##           develop    #1620      +/-   ##
===========================================
- Coverage    97.99%   97.99%   -0.01%     
===========================================
  Files          328      327       -1     
  Lines        18676    18666      -10     
===========================================
- Hits         18301    18291      -10     
  Misses         375      375              

Impacted Files	Coverage Δ
pybamm/citations.py	100.00% <100.00%> (ø)
pybamm/models/submodels/porosity/__init__.py	100.00% <0.00%> (ø)
pybamm/models/submodels/interface/sei/base_sei.py	100.00% <0.00%> (ø)
...els/submodels/porosity/reaction_driven_porosity.py	100.00% <0.00%> (ø)
...ubmodels/interface/lithium_plating/base_plating.py	100.00% <0.00%> (ø)
...submodels/porosity/reaction_driven_porosity_ode.py

---

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[brosaplanella]

Looks good, thanks @chuckliu1979! Before merging, can you add a line to CHANGELOG under the bug fixes section explaining what you did?

[brosaplanella]

@all-contributors please add @chuckliu1979 for bug report and code

[allcontributors]

@brosaplanella

I've put up a pull request to add @chuckliu1979! 🎉

[chuckliu1979]

Looks good, thanks @chuckliu1979! Before merging, can you add a line to CHANGELOG under the bug fixes section explaining what you did?

sure. new commit added