core: tolerate errors in gemrc

lib/vagrant/bundler.rb

@@ -123,7 +123,15 @@ module Vagrant
 
       # Set a custom configuration to avoid loading ~/.gemrc loads and
       # /etc/gemrc and so on.
-      old_config = Gem.configuration
+      old_config = nil
+      begin
+        old_config = Gem.configuration
+      rescue Psych::SyntaxError
+        # Just ignore this. This means that the ".gemrc" file has
+        # an invalid syntax and can't be loaded. We don't care, because
+        # when we set Gem.configuration to nil later, it'll force a reload
+        # if it is needed.
+      end
       Gem.configuration = NilGemConfig.new
 
       # Use a silent UI so that we have no output