Update cacheMatrix.R

Pass a matrix in function a<-makeCacheMatrix(matrix(1:4,2,2) or any other matrix. The matrix does not have to be necessarily a square matrix.
then call function a$get()
after call cacheSolve(a)
This will compute the result for the given example as
   [,1] [,2]
[1,]   -2  1.5
[2,]    1 -0.5