Expression to_dot syntax error

[fzanollo]

It seems a typo was added in some cleaning of the expr.py file at commit Lint cleanup: expr.py, changing ' for ".

Solution: change

    def to_dot(self, name="EXPR"): # pragma: no cover
        """Convert to DOT language representation."""
        parts = ["graph", name, "{', 'rankdir=BT;"]

to

    def to_dot(self, name="EXPR"): # pragma: no cover
        """Convert to DOT language representation."""
        parts = ["graph", name, "{", "rankdir=BT;"]

I'm ready to create a pull request if it helps you at all, thank you for this useful library!

[cjdrake]

Nice find :). Yes, please create a pull request.