docs(observable): update comparison table for consistency

Consistency in comparison table

doc/observable.md

@@ -4,7 +4,7 @@ Observables are lazy Push collections of multiple values. They fill the missing
 
 | | Single | Multiple |
 | --- | --- | --- |
-| **Pull** | [`Function`](https://developer.mozilla.org/en-US/docs/Glossary/Function) | [Iterator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols) |
+| **Pull** | [`Function`](https://developer.mozilla.org/en-US/docs/Glossary/Function) | [`Iterator`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols) |
 | **Push** | [`Promise`](https://developer.mozilla.org/en-US/docs/Mozilla/JavaScript_code_modules/Promise.jsm/Promise) | [`Observable`](../class/es6/Observable.js~Observable.html) |
 
 **Example.** The following is an Observable that pushes the values `1`, `2`, `3` immediately (synchronously) when subscribed, and the value `4` after one second has passed since the subscribe call, then completes: