Fix for #99 (#100)

fixes a failure with rbenv:build when the same version of rubygems
is used in different version of ruby.

manifests/build.pp

@@ -155,7 +155,7 @@
   # a series of issues like
   # https://bundler.io/blog/2019/05/14/solutions-for-cant-find-gem-bundler-with-executable-bundle.html.
   if $rubygems_version {
-    exec { "rubygems-${rubygems_version}":
+    exec { "rubygems-${rubygems_version}-for-${title}":
       command     => "gem update --system ${rubygems_version}",
       environment => ["RBENV_ROOT=${install_dir}"],
       require     => Exec["rbenv-install-${title}"],

spec/defines/build_spec.rb

@@ -47,7 +47,7 @@
         }
       end
 
-      it { is_expected.to contain_exec('rubygems-3.2.1') }
+      it { is_expected.to contain_exec('rubygems-3.2.1-for-2.0.0-p247') }
     end
 
     context 'with global => true' do