Fix CDN links (#3454)

README.md

@@ -14,7 +14,7 @@ Plottable is used and developed at [Palantir Technologies](http://palantir.com/)
 - Get Plottable:
   - npm: `npm install --save plottable`
   - yarn: `yarn add plottable`
-  - [unpkg](https://unpkg.com/plottable/plottable.min.js)
+  - [jsdelivr](https://cdn.jsdelivr.net/npm/plottable@3/plottable.min.js)
 - [Check out examples](http://plottablejs.org/examples/)
 - [Read the tutorials](http://plottablejs.org/tutorials/)
 - [Visit the website, plottablejs.org](http://plottablejs.org/)

quicktests/overlaying/index.html

@@ -31,7 +31,7 @@
         <option value="realistic">Realistic</option>
       </select>
 
-      <input type="text" id="branch1" name="branch1" value="//unpkg.com/plottable@next/plottable.js" placeholder="1st url (default plottable@next)">
+      <input type="text" id="branch1" name="branch1" value="//cdn.jsdelivr.net/npm/plottable@next/plottable.min.js" placeholder="1st url (default plottable@next)">
       <input type="text" id="branch2" name="branch2" value="../../plottable.js" placeholder="2nd branch (default local)">
       <input id="render" type="submit" class="button" value="Compare!">
       <input id="expand" type="button" class="button" value="+" onclick="showSizeControls()">

webpackConfig/build.js

@@ -17,8 +17,8 @@ Licensed under MIT (https://github.com/palantir/plottable/blob/master/LICENSE)`;
  *
  * User adds two script tags to their html page:
  *
- *   <script src="//cdnjs.cloudflare.com/ajax/libs/d3/4.5.0/d3.js"></script>
- *   <script src="//unpkg.com/plottable/plottable.js"></script>
+ *   <script src="https://cdn.jsdelivr.net/npm/d3@4.5.0/build/d3.min.js"></script>
+ *   <script src="https://cdn.jsdelivr.net/npm/plottable/plottable.min.js"></script>
  *
  * And then references Plottable globally.
  *
@@ -28,8 +28,8 @@ Licensed under MIT (https://github.com/palantir/plottable/blob/master/LICENSE)`;
  *
  * require.config( {
  *   paths: {
- *     d3: "https://cdnjs.cloudflare.com/ajax/libs/d3/4.5.0/d3.min",
- *     plottable: "//unpkg.com/plottable/plottable.js"
+ *     d3: "https://cdn.jsdelivr.net/npm/d3@4.5.0/build/d3.min.js",
+ *     plottable: "//cdn.jsdelivr.net/npm/plottable/plottable.min.js"
  *   },
  *   shim: {
  *     "plottable": {