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

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 rust-lang#29999

src/libterm/terminfo/mod.rs

@@ -190,7 +190,7 @@ impl<T: Write + Send> Terminal for TerminfoTerminal<T> {
     fn reset(&mut self) -> io::Result<bool> {
         // are there any terminals that have color/attrs and not sgr0?
         // Try falling back to sgr, then op
-        let cmd = match ["sg0", "sgr", "op"]
+        let cmd = match ["sgr0", "sgr", "op"]
                             .iter()
                             .filter_map(|cap| self.ti.strings.get(*cap))
                             .next() {