Fix the spec to be closer to guidelines

rubygem-xml-simple.spec

@@ -19,20 +19,19 @@ Provides: rubygem(%{gem_name}) = %{version}
 A simple API for XML processing.
 
 %prep
+%setup -q -c -T
+%gem_install -n %{SOURCE0}
 
 %build
 
 %install
-rm -rf %{buildroot}
 mkdir -p %{buildroot}%{gem_dir}
-%gem_install -n %{SOURCE0}
+cp -a .%{gem_dir}/* \
+        %{buildroot}%{gem_dir}/
+
 chmod -x %{buildroot}/%{gem_libdir}/xmlsimple.rb
 
-%clean
-rm -rf %{buildroot}
-
 %files
-%defattr(-, root, root, -)
 %{gem_instdir}
 %doc %{gem_docdir}
 %{gem_cache}