[Menu] Add a Dropdown example

• I have searched the issues of this repository and believe that this is not a duplicate.

Expected Behavior

Since Menu inherited from Popover, we should be able to change the value of anchorOrigin.

Current Behavior

Changing the property vertical of anchorOrigin change nothing. The Menu is still attached to the top of the anchor. horizontal property works great.

Steps to Reproduce

https://codesandbox.io/s/6nllq0zzlz

SimpleMenu doesn’t take into accounts the vertical property of anchorOrigin. SimplePopover is the same code, with Menu replaced with Popover (and the expected behavior).

Your Environment

Tech	Version
Material-UI	1.0.0-beta.38
React	16.2.0
browser	Chrome 65

[oliviertassinari]

        <Menu
          anchorEl={anchorEl}
          anchorOrigin={{
            vertical: "bottom",
            horizontal: "right"
          }}
+         getContentAnchorEl={null}

https://codesandbox.io/s/x8k6446oz

[micksatana]

The example having both anchorOrigin and transformOrigin

<Menu
  anchorOrigin={{
    vertical: 'top',
    horizontal: 'right',
  }}
  transformOrigin={{
    vertical: 'top',
    horizontal: 'right',
  }}

In my case, I remove transformOrigin and it works!

<Menu
  anchorOrigin={{
    vertical: 'top',
    horizontal: 'right',
  }}

Hope this helps someone