Bump minor version on driver and increase the current firmware version

[corot]

Due to issue #249.

CURRENT_FIRMWARE_MINOR_VERSION changes to 2.

This will make a warning log advising to update firmware at driver startup.

[corot]

Confirm that issue #249 is ok....

[stonier]

Just confirming...

This will advise on startup but not stop the program (i.e. just ROS_INFO/ROS_WARN or something?).

Was this the behaviour of existing code?

[corot]

As you said, you will see this warning:

sig_warn.emit("Robot firmware is outdated; we suggest you to upgrade it " \
                      "to benefit from the latest features. Consult how-to on: "  \
                      "http://kobuki.yujinrobot.com/documentation/howtos/upgrading-firmware");

[corot]

But I will add an specific message in case you call set/get PID methods

[stonier]

Ah...we did good!