Update convnet.md

Author: astonzhang

units/convnet.md

@@ -22,11 +22,11 @@
 
 ## Content
 
-* [Convolutional Neural Networks](http://en.diveintodeeplearning.org/chapter_convolutional-neural-networks/why-conv.html)
-* [Convolutions](http://en.diveintodeeplearning.org/chapter_convolutional-neural-networks/conv-layer.html)
-* [Padding and Strides](http://en.diveintodeeplearning.org/chapter_convolutional-neural-networks/padding-and-strides.html)
-* [Channels](http://en.diveintodeeplearning.org/chapter_convolutional-neural-networks/channels.html)
-* [Pooling](http://en.diveintodeeplearning.org/chapter_convolutional-neural-networks/pooling.html)
+* [Convolutional Neural Networks](https://d2l.ai/chapter_convolutional-neural-networks/why-conv.html)
+* [Convolutions](https://d2l.ai/chapter_convolutional-neural-networks/conv-layer.html)
+* [Padding and Strides](https://d2l.ai/chapter_convolutional-neural-networks/padding-and-strides.html)
+* [Channels](https://d2l.ai/chapter_convolutional-neural-networks/channels.html)
+* [Pooling](https://d2l.ai/chapter_convolutional-neural-networks/pooling.html)
 
 ## Videos