Update cachematrix.R

# Example usage:
# > x <- matrix(rnorm(16), nrow = 4) // Create a matrix x
# > cx <- makeCacheMatrix(x) // Create our special matrix
# > cx$get() // Return the matrix
# > cacheSolve(cx) // Return the inverse
# > cacheSolve(cx) // Call the 2nd time, so return
# // the cached inverse