Update tests to work with new interpose function

Author: HarryStevens

README.md

@@ -7,7 +7,7 @@ Calculate statistical regressions from two-dimensional data. [![Build Status](ht
 If you use NPM, `npm install d3-regression`. Otherwise, download the [latest release](https://github.com/HarryStevens/d3-regression/raw/master/dist/d3-regression.zip). AMD, CommonJS, and vanilla environments are supported. In vanilla, a d3 global is exported:
 
 ```html
-<script src="https://unpkg.com/d3-regression@1.3.0/dist/d3-regression.min.js"></script>
+<script src="https://unpkg.com/d3-regression@1.3.1/dist/d3-regression.min.js"></script>
 <script>
 
 const regression = d3.regressionLinear()

dist/d3-regression.js

@@ -1,4 +1,4 @@
-// https://github.com/HarryStevens/d3-regression#readme Version 1.2.8. Copyright 2019 Harry Stevens.
+// https://github.com/HarryStevens/d3-regression#readme Version 1.3.0. Copyright 2019 Harry Stevens.
 (function (global, factory) {
   typeof exports === 'object' && typeof module !== 'undefined' ? factory(exports) :
   typeof define === 'function' && define.amd ? define(['exports'], factory) :
@@ -126,7 +126,8 @@
   // returns a smooth line.
 
   function interpose(xmin, xmax, predict) {
-    var precision = .01,
+    var l = Math.log(xmax - xmin) * Math.LOG10E + 1 | 0;
+    var precision = 1 * Math.pow(10, -l / 2 - 1),
         maxIter = 1e4;
     var points = [px(xmin), px(xmax)],
         iter = 0;