Update serialport from 1.1.0 => 1.3.1.

[lukemcfarlane]

Installing firmata fails using ruby-2.2.2 due to old version of serialport, so this PR fixes that issue.

Test results:

# Running:

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Fabulous run in 0.006417s, 2804.8336 runs/s, 2493.1854 assertions/s.

18 runs, 16 assertions, 0 failures, 0 errors, 0 skips