### 5.43.17 Add a row to another row : rowAdd

rowAdd takes three arguments : a matrix A and two integers
n1 and n2.

rowAdd returns the matrix obtained by replacing in A, the row of index
n2 by the sum of the rows of index n1 and n2.

Input :

rowAdd([[1,2],[3,4]],0,1)

Output :

[[1,2],[4,6]]