BUG: Fix plt.close() calls and incorrect imports

[nawtrey]

• Fix locations of calls to plt.close() in plotting.py

• Fix sympy parser import in calculations.py

[codecov[bot]]

Codecov Report

Merging #37 (9e73b0e) into master (3a25773) will decrease coverage by 0.92%. The diff coverage is 22.22%.

@@            Coverage Diff             @@
##           master      #37      +/-   ##
==========================================
- Coverage   98.94%   98.02%   -0.93%     
==========================================
  Files           9        9              
  Lines         758      759       +1     
==========================================
- Hits          750      744       -6     
- Misses          8       15       +7     

Impacted Files	Coverage Δ
kda/plotting.py	93.06% <0.00%> (-3.47%)	:arrow_down:
kda/calculations.py	99.52% <100.00%> (+<0.01%)	:arrow_up:

[nawtrey]

CI is passing, merging.