Add algorithm to find lcm (least common multiple).

[msk4862]

Algorithm for finding lcm(least common multiple) is not added.

[shubhamkakkar]

I am taking this issue

[anshal570]

I want to work on this issue.

[Kunal614]

I want to work on this issue.

[Kunal614]

I want to work on this issue.

i have done a pull request for this
#526

[karpit14]

I want to pull request this as i am interested to work on this.

[fhlasek]

Resolved by now
https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/math/least_common_multiple.cpp