jsx-wrap-multilines now catches single missing newlines

[MrHen]

Fixes #1965. The only interesting question is how the fixer should treat the newlines. I chose to make it add a new line if there was exactly zero after or before the parens. This means:

  var Hello = createReactClass({
    render: function() {
      return (<div>
        <p>Hello {this.props.name}</p>
      </div>
      );
    }
  });

Fixes to:

  var Hello = createReactClass({
    render: function() {
      return (
<div>
        <p>Hello {this.props.name}</p>
      </div>
      );
    }
  });

---

And:

  var Hello = createReactClass({
    render: function() {
      return (<div>
        <p>Hello {this.props.name}</p>
      </div>

      );
    }
  });

Fixes to:

  var Hello = createReactClass({
    render: function() {
      return (
<div>
        <p>Hello {this.props.name}</p>
      </div>

      );
    }
  });

---

The alternative would be to make exactly one newline regardless of how many there were before -- but I assumed such a behavior should be its own rule instead of attached to this rule.

[ljharb]

These extra newlines here seem odd - why is this allowed to be here?

[MrHen]

See my earlier comment:
#1984 (comment)

My first attempts at fixing this caused extraneous newlines to disappear which seemed like an undesired side-effect of this particular rule. The extra newline isn't being added by the fix -- its in the original test condition. The test is making sure the extra newline is not being stripped.

[ljharb]

That makes sense (although I’d want it stripped, this probably isn’t the rule for it)

[MrHen]

Thanks for the review @ljharb. What's the next step to getting this merged? Anything I need to do?