Invoke fir error

/home/vagrant/.rvm/gems/ruby-2.1.5/gems/fir-repl-0.1.1/lib/fir/repl_state.rb:6:in `require_relative': /home/vagrant/.rvm/gems/ruby-2.1.5/gems/fir-repl-0.1.1/lib/fir/indent.rb:191: syntax error, unexpected '.' (SyntaxError)
      !(OPTIONAL_DO_TOKENS.include?(stack.last&.word) &&
                                                ^
/home/vagrant/.rvm/gems/ruby-2.1.5/gems/fir-repl-0.1.1/lib/fir/indent.rb:192: syntax error, unexpected '.'
        (token.position.y == stack.last&.position&.y))
                                         ^
/home/vagrant/.rvm/gems/ruby-2.1.5/gems/fir-repl-0.1.1/lib/fir/indent.rb:197: syntax error, unexpected '.'
      stack.last&.word != 'when'
                  ^
/home/vagrant/.rvm/gems/ruby-2.1.5/gems/fir-repl-0.1.1/lib/fir/indent.rb:202: syntax error, unexpected '.'
      return false unless stack.last&.word == 'when'
                                      ^
/home/vagrant/.rvm/gems/ruby-2.1.5/gems/fir-repl-0.1.1/lib/fir/indent.rb:208: syntax error, unexpected '.'
      return false unless stack.last&.word == 'when'
                                      ^
/home/vagrant/.rvm/gems/ruby-2.1.5/gems/fir-repl-0.1.1/lib/fir/indent.rb:214: syntax error, unexpected '.'
      return false unless stack.last&.word == 'if'
                                      ^
/home/vagrant/.rvm/gems/ruby-2.1.5/gems/fir-repl-0.1.1/lib/fir/indent.rb:224: dynamic constant assignment
    Token = Struct.new(:word, :position)
           ^
/home/vagrant/.rvm/gems/ruby-2.1.5/gems/fir-repl-0.1.1/lib/fir/indent.rb:225: dynamic constant assignment
    Position = Struct.new(:x, :y)
              ^
/home/vagrant/.rvm/gems/ruby-2.1.5/gems/fir-repl-0.1.1/lib/fir/indent.rb:226: dynamic constant assignment
    IndentBlock = Struct.new(:indents, :executable?)
                 ^
/home/vagrant/.rvm/gems/ruby-2.1.5/gems/fir-repl-0.1.1/lib/fir/indent.rb:228: syntax error, unexpected end-of-input, expecting keyword_end
        from /home/vagrant/.rvm/gems/ruby-2.1.5/gems/fir-repl-0.1.1/lib/fir/repl_state.rb:6:in `<top (required)>'
        from /home/vagrant/.rvm/gems/ruby-2.1.5/gems/fir-repl-0.1.1/lib/fir.rb:8:in `require_relative'
        from /home/vagrant/.rvm/gems/ruby-2.1.5/gems/fir-repl-0.1.1/lib/fir.rb:8:in `<top (required)>'
        from /home/vagrant/.rvm/rubies/ruby-2.1.5/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require'
        from /home/vagrant/.rvm/rubies/ruby-2.1.5/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require'
        from /home/vagrant/.rvm/gems/ruby-2.1.5/gems/fir-repl-0.1.1/bin/fir:5:in `<top (required)>'
        from /home/vagrant/.rvm/gems/ruby-2.1.5/bin/fir:23:in `load'
        from /home/vagrant/.rvm/gems/ruby-2.1.5/bin/fir:23:in `<main>'
        from /home/vagrant/.rvm/gems/ruby-2.1.5/bin/ruby_executable_hooks:15:in `eval'
        from /home/vagrant/.rvm/gems/ruby-2.1.5/bin/ruby_executable_hooks:15:in `<main>'