[ENH] Added shortest path override

[liuzhenqi77]

Override some functions from bct, because they are too slow.

[codecov-commenter]

Codecov Report

Merging #118 (ae96e7c) into master (3b4b5df) will decrease coverage by 0.25%. The diff coverage is 48.38%.

@@            Coverage Diff             @@
##           master     #118      +/-   ##
==========================================
- Coverage   72.09%   71.83%   -0.26%     
==========================================
  Files          26       27       +1     
  Lines        1903     1946      +43     
==========================================
+ Hits         1372     1398      +26     
- Misses        531      548      +17     

Impacted Files	Coverage Δ
netneurotools/metrics.py	39.75% <48.38%> (+3.90%)	:arrow_up:
netneurotools/colors.py	92.30% <0.00%> (ø)

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