travis: install genmsg which is required by genmsp.

Signed-off-by: Michael Hope <mlhx@google.com>

.travis.yml

@@ -29,7 +29,10 @@ install:
   - sudo apt-get install build-essential git libc6-i386
   - tar -xf gcc-arm-none-eabi-4_8-2014q3-20140805-linux.tar.bz2
   - export PATH=$PATH:$PWD/gcc-arm-none-eabi-4_8-2014q3/bin
-   
+  - sudo apt-get install -qq python-catkin-pkg python-empy
+  - git clone https://github.com/ros/genmsg
+  - cd genmsg && sudo python setup.py install && cd ..
+
 before_script: arm-none-eabi-gcc --version
 script: ./.travis.sh
 
@@ -38,4 +41,4 @@ cache: apt
 notifications:
   irc: "chat.freenode.net#cleanflight"
   use_notice: true
-  skip_join: true
+  skip_join: true