build failed for examples

[topelinux]

when build example with following command

cargo build --example i2cdetect

it show following error

error[E0463]: can't find crate for `log`
  --> examples/i2cdetect.rs:10:1
   |
10 | extern crate log;
   | ^^^^^^^^^^^^^^^^^ can't find crate

error: aborting due to previous error