Fix default terminfo code for reset (sg0 -> sgr0)

[martijnvermaat]

Resetting the terminal should first try sgr0 (as per the comment), not
sg0 which I believe to be a typo.

This will at least fix rustc output in Emacs terminals (e.g., ansi-term)
with TERM=eterm-color which does not provide the next fallback sgr. In
such a terminal, the final fallback op (\e[39;49) is used which
resets only colors, not all attributes. This causes all text to be
printed in bold from the first string printed in bold by rustc onwards,
including the terminal prompt and the output from all following commands.

The typo seems to have been introduced by #29999

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @alexcrichton (or someone else) soon.

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[alexcrichton]

@bors: r+

Thanks!

[bors]

📌 Commit 1825f80 has been approved by alexcrichton