Update toml-rs

TOML recently grew multiline string literals as well as literal strings with no
escaping, which can be used instead of the hokey escape_path() function.
auto merge of #206 : alexcrichton/cargo/update-toml, r=wycats

TOML recently grew multiline string literals as well as literal strings with no
escaping, which can be used instead of the hokey escape_path() function.