Rename "QuantitiveScale" to "QuantitativeScale" for consistency 

Adds consistency with d3's API docs and common usage of the english language.

Close #2573

As copied from the issue:
Right now in d3.d.ts the base class for numerical scales is called "QuantitiveScale". However, in the D3 API reference, such scales are described as "Quantitative Scales" (just look at the spelling in this URL: https://github.com/mbostock/d3/wiki/Quantitative-Scales). Also, Google Trends shows that the word "Quantitative" is far more frequently used than "Quantitive" (http://www.google.com/trends/explore#q=quantitive%2C%20quantitative&cmpt=q) although they have the same meaning (http://grammarist.com/usage/quantitative-quantitive/)