fix issue with HW1 link

Author: msneubauer

_sources/homework/Homework_01.ipynb

@@ -577,7 +577,7 @@
     "\n",
     "The computational cost of each method depends differently on the values of $N$ and $D$, so the most efficient method will depend on the shape of the input data $X$. There are also numerical considerations: the matrices $C$ and $D$ should be [positive definite](https://en.wikipedia.org/wiki/Positive-definite_matrix) in order to guarantee positive eigenvalues, but this will not be true for $C$ if $N < D$ or for $D$ if $N > D$.\n",
     "\n",
-    "Implement the function below to calculate the eigenvectors and eigenvalues of a square input matrix using a suitable function from [np.linalg](https://docs.scipy.org/doc/numpy-1.13.0/reference/routines.linalg.html).  The results should be sorted in order of decreasing eigenvalues, as needed by PCA. Hint: `M[::-1]` reverses the rows of a 2D array `M` (more info [here](https://docs.scipy.org/doc/numpy-dev/user/quickstart.html#indexing-slicing-and-iterating))."
+    "Implement the function below to calculate the eigenvectors and eigenvalues of a square input matrix using a suitable function from [np.linalg](https://docs.scipy.org/doc/numpy-1.13.0/reference/routines.linalg.html).  The results should be sorted in order of decreasing eigenvalues, as needed by PCA. Hint: `M[::-1]` reverses the rows of a 2D array `M` (more info [here](https://numpy.org/doc/stable/user/quickstart.html#indexing-slicing-and-iterating))."
    ]
   },
   {