feat: Update lesson 4

Author: computationalcore

.gitignore

@@ -9,6 +9,7 @@
 *.user
 *.userosscache
 *.sln.docstates
+*.vscode
 
 # User-specific files (MonoDevelop/Xamarin Studio)
 *.userprefs

README.md

@@ -20,8 +20,8 @@ I also provided the estimated time required to complete each lesson, a link to t
 | OpenCV fundamentals       | 20 min | [Open](https://github.com/computationalcore/introduction-to-opencv/blob/master/notebooks/1-Fundamentals.ipynb) | [Open](https://colab.research.google.com/github/computationalcore/introduction-to-opencv/blob/master/notebooks/1-Fundamentals.ipynb) |
 | Image stats and image processing       | 20 min | [Open](https://github.com/computationalcore/introduction-to-opencv/blob/master/notebooks/2-Image_stats_and_image_processing.ipynb) | [Open](https://colab.research.google.com/github/computationalcore/introduction-to-opencv/blob/master/notebooks/2-Image_stats_and_image_processing.ipynb) |
 | Features in computer vision       | 20 min | [Open](https://github.com/computationalcore/introduction-to-opencv/blob/master/notebooks/3-Features.ipynb) | [Open](https://colab.research.google.com/github/computationalcore/introduction-to-opencv/blob/master/notebooks/3-Features.ipynb) |
-| Face Detection      | 5 min | [Open](https://github.com/computationalcore/introduction-to-opencv/blob/master/notebooks/4-face_detection.ipynb) | [Open](https://colab.research.google.com/github/computationalcore/introduction-to-opencv/blob/master/notebooks/4-face_detection.ipynb) |
-| **Total** | **65 min** |  |  |
+| Cascade Classification      | 20 min | [Open](https://github.com/computationalcore/introduction-to-opencv/blob/master/notebooks/4-Cascade_classification.ipynb) | [Open](https://colab.research.google.com/github/computationalcore/introduction-to-opencv/blob/master/notebooks/4-Cascade_classification.ipynb) |
+| **Total** | **80 min** |  |  |
 
 ## License