[root@fab SPECS]# yum install dnf -y
Loaded plugins: fastestmirror, langpacks, refresh-packagekit
Loading mirror speeds from cached hostfile
 * rawhide: mirrors.yun-idc.com
 * rpmfusion-free-rawhide: mirrors.163.com
 * rpmfusion-nonfree-rawhide: mirrors.163.com
Resolving Dependencies
--> Running transaction check
---> Package dnf.noarch 0:0.3.11-1.git7d717c7.fc20 will be installed
--> Processing Dependency: python-librepo = 0.0.5 for package: dnf-0.3.11-1.git7d717c7.fc20.noarch
--> Finished Dependency Resolution
Error: Package: dnf-0.3.11-1.git7d717c7.fc20.noarch (rawhide)
           Requires: python-librepo = 0.0.5
           Installed: python-librepo-1.0.0-1.fc21.i686 (@rawhide)
               python-librepo = 1.0.0-1.fc21
 You could try using --skip-broken to work around the problem
 You could try running: rpm -Va --nofiles --nodigest


Seems someone just push dnf update at Aug 28, so I hope you can update the deps or modify the spec.