Indices of polynomial regression components are wrong in interactive examples

[Wookai]

All the p and p bar symbols in the interactive visualization of the polynomial regression model have index 1, but the index should range from 1 to 6.

For example, the first interactive plots says:

-2.00p_1 + -2.00p_1 + -2.00p_1 + -2.00p_1 + -2.00p_1 + -2.00p_1 = model

but I think it should be:

-2.00p_1 + -2.00p_2 + -2.00p_3 + -2.00p_4 + -2.00p_5 + -2.00p_6 = model

The other two interactive examples are the same (indices are wrong).

[diego898]

This also mentioned in #91