Fixed issue with insert in BinarySearchTree

[Aimaanhasan]

References to other Issues or PRs or Relevant literature

See #235 (comment) of PR #235

Brief description of what is fixed or changed

insert in BinarySearchTree assumes root as 0 and starts with 0 by initializing prev_node as shown below:

pydatastructs/pydatastructs/trees/binary_trees.py

Line 221 in 4452dc8

new_node, prev_node, flag = TreeNode(key, data), 0, True

.

However, this is not a case if the tree is rotated, root can be changed from 0.

[codecov]

Codecov Report

Merging #259 into master will not change coverage.
The diff coverage is 100.000%.

@@            Coverage Diff            @@
##            master      #259   +/-   ##
=========================================
  Coverage   98.563%   98.563%           
=========================================
  Files           24        24           
  Lines         2228      2228           
=========================================
  Hits          2196      2196           
  Misses          32        32           

Impacted Files	Coverage Δ
pydatastructs/trees/binary_trees.py	97.033% <100.000%> (ø)

[czgdp1807]

Ah I see, that's a very trivial mistake and I did that. Thanks for fixing.