Merge pull request #78 from dronekit/rr_update_circleci_build

update circleci build script

circle.yml

@@ -1,16 +1,11 @@
 machine:
+  pre:
+    - sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-4.9 20
   environment:
     LOGANALYZE_DIRPATH_LOG: dronekit-la-testdata-3dr
 
 dependencies:
   pre:
-    - sudo apt-get update -y
-    - sudo apt-get install -y build-essential
-    - sudo apt-get install -y g++
-    - sudo apt-get install -y libjsoncpp-dev libjsoncpp0
-    - sudo rm /usr/bin/g++ /usr/bin/gcc
-    - sudo ln -s /usr/bin/g++-4.9 /usr/bin/g++
-    - sudo ln -s /usr/bin/gcc-4.9 /usr/bin/gcc
     - git submodule init
     - git submodule update