Update 10.4-test-utils.md

This adds minimal valid event data to the Simulate.change example for a text input field.
Update tutorial language to be more explicit.

The word "Friends" does establish a relationship however it does not fit in the vernacular of react. 
This change makes the phrase more explicit and more familiar.
Merge pull request #2554 from samccone/patch-1

Update tutorial language to be more explicit.
Merge pull request #2544 from mjul/patch-1

Update 10.4-test-utils.md
Summary:
Currently, `ReactUpdates` updates dirty components in increasing order of mount depth. However, mount depth is only relative to the component passed into `React.render`. This breaks down for components that invoke `React.render` as an implementation detail because the child components will be updated before the parent component.

This fixes the problem by using the order in which components are mounted (instead of their depth). The mount order transcends component trees (rooted at `React.render` calls).

Reviewers: @sebmarkbage @zpao

Test Plan:
Ran unit tests successfully:

```
npm run jest
```
Merge pull request #2570 from yungsters/updates

Update Dirty Components in Mount Ordering
Replace `mountDepth` with `isTopLevel`

Summary:
After #2570, `mountDepth` is only used to enforce that `setProps` and `replaceProps` is only invoked on the top-level component. This replaces `mountDepth` with a simpler `isTopLevel` boolean set by `ReactMount` which reduces the surface area of the internal API and removes the need to thread `mountDepth` throughout React core.

Reviewers: @sebmarkbage @zpao

Test Plan:
Ran unit tests successfully:

```
npm run jest
```
Merge pull request #2571 from yungsters/cleanup

Replace `mountDepth` with `isTopLevel`
Removed context paremeter to renderToString/renderToStaticMarkup.