Ids are missing if the FormattedMessage uses the same defaultMessage

[scottdickerson]

• version: 3.3.0
• node version:
• npm (or yarn) version:

Do you want to request a feature or report a bug?: Bug

What is the current behavior?: For FormattedMessage if the FormattedMessage is placed directly inside a span, the ID fails to generate for the second component and react-intl will throw the invariant missing ID message when the component is rendered.

This should reproduce the error

<span>
<FormattedMessage defaultMessage='Hi There' />
</span>

What is the expected behavior?: All FormattedMessages would successfully generate an ID

Suggested solution: I've worked around this by hardcoding an id in the specific messages that were failing to generate an ID or by using <FormattedMessage tagName="span"/>