Allow `require: true` as an alias for `require: <name>`

Here's my use-case:

```ruby
# Don't require debugger if using RubyMine
gem 'debugger', require: !ENV['RM_INFO']
```

------------------

Currently we have to write:

```ruby
gem 'debugger', require: (ENV['RM_INFO'] ? false : 'debugger')
```

or

```ruby
gem 'debugger', {}.merge(ENV['RM_INFO'] ? {require: false} : {})
```