fixup! Bring back bundler/rubygems updates for Ruby 2.3+

Author: pirj

travis/script/predicate_functions.sh

@@ -54,6 +54,14 @@ function is_mri_2plus {
   fi
 }
 
+function is_ruby_23_plus {
+  if ruby -e "exit(RUBY_VERSION.to_f >= 2.3)"; then
+    return 0
+  else
+    return 1
+  fi
+}
+
 function is_ruby_25_plus {
   if ruby -e "exit(RUBY_VERSION.to_f >= 2.5)"; then
     return 0

travis/script/update_rubygems_and_install_bundler

@@ -2,7 +2,7 @@
 set -e
 source script/functions.sh
 
-if is_ruby_25_plus; then
+if is_ruby_23_plus; then
   yes | gem update --system
   yes | gem install bundler
 else