Don't log files as they're extracted from tarball

The `-v` option for tar has been here since the beginning of ruby-build,
but it's not really informative to see a list of files in the log as the
list of files is guaranteed to be the same across machines since we do
checksums.

bin/ruby-build

@@ -277,7 +277,7 @@ fetch_tarball() {
     fi
   fi
 
-  local tar_args="xzvf"
+  local tar_args="xzf"
   local package_filename="${package_name}.tar.gz"
 
   if [ "$package_url" != "${package_url%bz2}" ]; then