Update Regression_tuner.ipynb

[Odin-Data]

Changes have been made to the build_model function, adding the input layer definition to the sequential model with input_shape. Additionally, the kerastuner library has been updated as keras_tuner, as it is obsolete.

[ezponda]

Thanks @Odin-Data , remember that input_shape(7,) should only be in the first layer, If you put it inside the loop, you are including it to every layer