Battery Monitor 2 Pixhawk 2.1 Current pin

#### Issue details
MP is setting Battery Monitor 2 current pin to 12 for Pixhawk 2.1
Should be pin 14

#### Version
1.3.5.6 1.3.6672.30243
#### Platform
[ ] All
[ ] AntennaTracker
[ * ] Copter
[ ] Plane
[ ] Rover
[ ] Sub

#### Airframe type
_What type of airframe (flying wing, glider, hex, Y6, octa etc)_

#### Hardware type
_What autopilot hardware was used? (pixhawk, pixracer, PX4FMU etc)_

#### Logs
_Please provide a link to any relevant logs that show the issue_

No file or test is named. Start by searching the Mission Planner code for the Pixhawk 2.1 Battery Monitor 2 current-pin assignment and compare it with the hardware mapping described here. Done means the Copter configuration uses pin 14 rather than pin 12.

Written by the indexing model from the issue text.