NameError: `@reply-type' is not allowed as an instance variable name

When attempting to access the content of a message with a single body_part, I receive the following error:

```
NameError: `@reply-type' is not allowed as an instance variable name
```

To recreate in ruby 1.9.3, contextio-ruby gem 1.3.0:

```
> message = account.messages.first
> message.body_parts.count
 => 1
> message.body_parts.first
NameError: `@reply-type' is not allowed as an instance variable name
	from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/contextio-1.3.0/lib/contextio/body_part.rb:27:in `instance_variable_set'
	from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/contextio-1.3.0/lib/contextio/body_part.rb:27:in `block in initialize'
	from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/contextio-1.3.0/lib/contextio/body_part.rb:26:in `each'
	from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/contextio-1.3.0/lib/contextio/body_part.rb:26:in `initialize'
	from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/contextio-1.3.0/lib/contextio/api/resource_collection.rb:52:in `new'
	from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/contextio-1.3.0/lib/contextio/api/resource_collection.rb:52:in `block in each'
	from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/contextio-1.3.0/lib/contextio/api/resource_collection.rb:51:in `each'
	from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/contextio-1.3.0/lib/contextio/api/resource_collection.rb:51:in `each'
	from (irb):29:in `first'
	from (irb):29
	from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/railties-3.2.11/lib/rails/commands/console.rb:47:in `start'
	from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/railties-3.2.11/lib/rails/commands/console.rb:8:in `start'
	from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/railties-3.2.11/lib/rails/commands.rb:41:in `<top (required)>'
	from script/rails:6:in `require'
	from script/rails:6:in `<main>'
```

This occurs on about half of the messages I attempt it on. The other half work without issue. 

I thought it might be related to types available, but I can not test this as calls like this fail if the body_part.first.content call fails:

```
1.9.3p194 :044 > message.body_parts.first.type
NameError: `@reply-type' is not allowed as an instance variable name
```