Update cisco-config-parse.rb

error occurred when the config command like "switchport"

C:/Ruby193/lib/ruby/gems/1.9.1/gems/cisco-config-parse-0.0.5/lib/cisco-config-pa
rse.rb:94:in `p_config_interface_switchport': undefined method `split' for nil:N
ilClass (NoMethodError)
        from C:/Ruby193/lib/ruby/gems/1.9.1/gems/cisco-config-parse-0.0.5/lib/ci
sco-config-parse.rb:49:in `parse_config'
        from C:/Ruby193/lib/ruby/gems/1.9.1/gems/cisco-config-parse-0.0.5/lib/ci
sco-config-parse.rb:16:in `block in parse'
        from C:/Ruby193/lib/ruby/gems/1.9.1/gems/cisco-config-parse-0.0.5/lib/ci
sco-config-parse.rb:9:in `each'
        from C:/Ruby193/lib/ruby/gems/1.9.1/gems/cisco-config-parse-0.0.5/lib/ci
sco-config-parse.rb:9:in `parse'
        from parse_conf.rb:4:in `<main>'