R CMD check warning on Windows

[stewid]

New warning on Windows https://ci.appveyor.com/project/karthik/git2r/build/1.0.1171#L336

 R CMD check git2r_0.13.1.9000.tar.gz --no-manual --as-cran --install-args=--build --no-multiarch
* using log directory 'C:/projects/git2r/git2r.Rcheck' 
* using R Under development (unstable) (2016-03-09 r70299) 
* using platform: i386-w64-mingw32 (32-bit)
:
:
* checking whether package 'git2r' can be installed ... WARNING
Found the following significant warnings: 
  libgit2/src/config.c:602:2: warning: too many arguments for format [-Wformat-extra-args]
  libgit2/src/odb.c:56:2: warning: too many arguments for format [-Wformat-extra-args]

Not sure why this happens now. These lines of code has not changed recently.