Fix typo

Author: achiefa

doc/nntraining.tex

@@ -72,7 +72,7 @@
   In this work, we develop a theoretical framework based on the
   Neural Tangent Kernel (NTK) to analyse the training dynamics of neural
   networks. This approach allows us to derive, under precise assumptions, an
-  analytical description of the neural networks evolution during training,
+  analytical description of the neural network evolution during training,
   enabling a quantitative understanding of the training process. 
   Having an analytical handle on the training dynamics allows us to clarify the
   role of the NN architecture and the impact of the experimental data in a