Fixing 'Visualizing Data' link in Readme
Fixing 'Visualizing Data' link in Readme

Readme's 'Visualizing Data' is giving wrong link due to rename of visualization python file.
RichHelle/data-science-from-scratch,Insight-book/data-science-from-scratch,joelgrus/data-science-from-scratch,fgiunta/data-science-from-scratch