the formatting type `t` is not in rustc 0.13.0-nightly version

for rustc 0.13.0-nightly (8bca470c5 2014-12-08 00:12:30 +0000) version, the formatting type `t` is not here, and will print error like this:
10:74 error: unknown format trait `t`
Merge pull request #297 from geekcraik/master

the formatting type `t` is not in rustc 0.13.0-nightly version