Add: Cousins in Binary Tree

[awesee]

No description provided.

[codecov-io]

Codecov Report

Merging #382 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #382   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files         132    133    +1     
  Lines        1364   1385   +21     
=====================================
+ Hits         1364   1385   +21

Impacted Files	Coverage Δ
...s/cousins-in-binary-tree/cousins_in_binary_tree.go	100% <100%> (ø)

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