bc98e9fbc2
Fix the return type in the comments. An old commit 082bfde41217 ("Fallout of std::str stabilization") removed the example of FromStr::from_str(), this commit adds it back. But the example of StrExt::parse() is still kept with an additinal note. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>