Hmm ... It's impossible ;-) This RPM doesn't exist on any FTP server

Provides :
pkgconfig(ruby-2.1)
ruby21-devel
ruby21-devel(x86-64)

Requires :

rpmlib(FileDigests) <= 4.6.0-1
rpmlib(CompressedFileNames) <= 3.0.4-1
gmp-devel
/usr/bin/pkg-config
rpmlib(PayloadIsXz) <= 5.2-1
libruby2_1-2_1 = 2.1.10
rpmlib(PayloadFilesHavePrefix) <= 4.0-1
libruby2.1.so.2.1()(64bit)

Content of RPM :
/usr/include/ruby-2.1.0
/usr/include/ruby-2.1.0/ruby
/usr/include/ruby-2.1.0/ruby.h
/usr/include/ruby-2.1.0/ruby/backward
/usr/include/ruby-2.1.0/ruby/backward/classext.h
/usr/include/ruby-2.1.0/ruby/backward/rubyio.h
/usr/include/ruby-2.1.0/ruby/backward/rubysig.h
/usr/include/ruby-2.1.0/ruby/backward/st.h
/usr/include/ruby-2.1.0/ruby/backward/util.h
/usr/include/ruby-2.1.0/ruby/config.h
/usr/include/ruby-2.1.0/ruby/debug.h
/usr/include/ruby-2.1.0/ruby/defines.h
/usr/include/ruby-2.1.0/ruby/digest.h
/usr/include/ruby-2.1.0/ruby/dl.h
/usr/include/ruby-2.1.0/ruby/encoding.h
/usr/include/ruby-2.1.0/ruby/intern.h
/usr/include/ruby-2.1.0/ruby/io.h
/usr/include/ruby-2.1.0/ruby/missing.h
/usr/include/ruby-2.1.0/ruby/oniguruma.h
/usr/include/ruby-2.1.0/ruby/re.h
/usr/include/ruby-2.1.0/ruby/regex.h
/usr/include/ruby-2.1.0/ruby/ruby.h
/usr/include/ruby-2.1.0/ruby/st.h
/usr/include/ruby-2.1.0/ruby/subst.h
/usr/include/ruby-2.1.0/ruby/thread.h
/usr/include/ruby-2.1.0/ruby/util.h
/usr/include/ruby-2.1.0/ruby/version.h
/usr/include/ruby-2.1.0/ruby/vm.h
/usr/include/ruby-2.1.0/x86_64-linux-gnu
/usr/include/ruby-2.1.0/x86_64-linux-gnu/ruby
There is 3 files more in these RPM.