serialport -> rubyserial, Travis CI Ruby version updates, Bundler restriction lift

[joealba]

• Switch from the serialport gem to the rubyserial gem - use rubyserial instead of serialport #46
• Update the versions of MRI Ruby that get tested in Travis to the latest supported versions
• Remove jruby from Travis, as it fails to build the serialport gem
• Remove the overly-strict restriction on the version of Bundler to help folks with more recent installs have an easier time contributing
• Whitespace-only: Make the gem dependency formatting consistent

[fmluizao]

Hi @joealba, thanks for your contribution!

About rubyserial, It seems to lack flush_input and flush_output and blocking read. I'm not sure if flushing is necessary, but blocking read is... did you test with a real device?

[joealba]

@fernandoluizao My apologies, I was relying on the comment in the RubySerial readme that its interface was "(mostly)" compatible with other implementations. I did not test on a real device.

[fmluizao]

I would love to switch to rubyserial, mostly for jruby compatibility... unfortunately I don't have a device with a serial port to test.

I'll cherry-pick the other commits, and leave the rubyserial change for later, until we can make sure rubyserial works without more changes.