Sort .gitignore.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
Use globs to ignore target directories.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
auto merge of #16194 : omasanori/rust/gitignore, r=alexcrichton

I also sorted lines in .gitignore. The file might include some obsoleted lines but I left.