Fix issue in 20.2.3 code

[alioh]

In 20.2 bias_modeling notebook, there is an issue with "Example: Linear Regression and Sine Waves" code, when you run it you will get "Expected 2D array, got scalar array instead".

To fix this issue, make the following changes to line 23:

• from: return Line(x_start, x_end, clf.predict(x_start)[0], clf.predict(x_end)[0])
• to: return Line(x_start, x_end, clf.predict([[x_start]])[0], clf.predict([[x_end]])[0])

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