Add convenience script to update Ruby

script/rbenv-install.sh

@@ -0,0 +1,15 @@
+#!/bin/bash
+#
+# Install our selected Ruby version defined in the .ruby-version file.
+#
+# If our ruby-build version is outdated and it can't build the version we want
+# then we try upgrading ruby-build and installing again.
+
+if rbenv install --skip-existing; then
+  echo "Ruby is installed."
+else
+  echo "Upgrading rbenv's ruby-build:"
+  git -C "$(rbenv root)"/plugins/ruby-build pull
+
+  rbenv install
+fi