Travis-CI: add vrubrain-v51 target (Copter)

.travis.yml

@@ -7,3 +7,4 @@ script:
   - cd ./ardupilot/ArduCopter && make configure && make && make px4-v2
   - cd ../ArduPlane  && make configure && make && make px4-v2
   - cd ../APMrover2  && make configure && make && make px4-v2
+  - cd ../ArduCopter && make configure && make && make vrubrain-v51

Tools/scripts/install-prereqs-ubuntu.sh

@@ -69,6 +69,10 @@ if [ ! -d PX4NuttX ]; then
     git clone https://github.com/diydrones/PX4NuttX.git
 fi
 
+if [ ! -d VRNuttX ]; then
+    git clone https://github.com/virtualrobotix/vrbrain_nuttx.git VRNuttX
+fi
+
 if [ ! -d $OPT/$ARM_ROOT ]; then
     (
         cd $OPT;