Fixed formatting.

The code block shows up inline without proper formatting without this
newline.

Signed-off-by: Noufal Ibrahim <noufal@nibrahim.net.in>
docs: Replace std::iterator with std::iter.
auto merge of #10248 : nibrahim/rust/docformatting, r=pcwalton

The code block shows up inline without proper formatting without this
newline.

Signed-off-by: Noufal Ibrahim <noufal@nibrahim.net.in>
auto merge of #10252 : huonw/rust/docs, r=alexcrichton