Dynamic wrapper

[ghost]

Adds a new prop wrapper.
default: "div"
supportedWrappers: span, div

Let the user define the wrapper for the Tooltip dynamically.
fixes -> #210

[wwayne]

I was thinking why don't just use <span> directly, I mean maybe I should use span as default wrapper, would it be better?

[ghost]

Well, yeah you can use span as the default, but it could mean some upgrading issues, for people who are rendering divs inside the tooltip in production. It's safer to keep div as the default.

Only span would be not better, because if you render blocks (div) inside inline (span) elements you'll get an error like #210

To have a choice is better ;)

[MatanBobi]

After reviewing this PR and its result,
I keep getting "wrapper" elements inside my html.
I think that its because of this:

https://github.com/dropfen/react-tooltip/blob/25aa42a2b8113aff21bb053f309d7ace9b937f93/src/index.js#L428

React doesnt render the variable wrapper as a div/span but as a DOM element.
I think its because that the variable isnt with capital letter so react doesnt see it as a component.

[huumanoid]

Yes, you are right! Thank you for your review!
Babel's react preset treats wrapper as a tag name, not as a component.
https://github.com/wwayne/react-tooltip/blob/master/standalone/react-tooltip.js#L843

If you change wrapper to Wrapper, everything is fine.
Could you make a PR, please?

Also, take a note that there is a linter error.

~/github/react-tooltip/src/index.js
  441:9  error  Empty components are self-closing  react/self-closing-comp