amp-imgur "imgur.com refused to connect"

## What's the issue?

The amp-imgur component fails (no content) when setting data-imgur-id to the ID displayed on imgur.com.

## How do we reproduce the issue?

```html

```

## What browsers are affected?

* Google Chrome Version 81.0.4044.122 (Official Build) (64-bit)
* Probably all

## Which AMP version is affected?

`Powered by AMP ⚡ HTML – Version 2004172112280`

## How to fix the issue (note the `a/` preceding the ID):

```html

```

It took me a while to figure this out, digging through closed issues. This is either a documentation issue (remember to add `a/` in front of the ID provided by imgur.com) or a code issue (programmatically add `a/` in front of the ID before making the request to imgur.com).

Start by locating the amp-imgur component implementation and its documentation, then reproduce the supplied example with data-imgur-id="wFKGNae". Determine whether the component should accept the displayed Imgur ID or whether the documentation must require the a/ prefix; done means the documented example renders content consistently.

Written by the indexing model from the issue text.