message: travis: correct fix_style make target
diff: @@ -5,7 +5,7 @@ set -e
  make BUILD_TYPE=Debug run_unit_tests -j4
  make install
  make docs
  -make fix-style
  +make fix_style
  (cd example/takeoff_land && mkdir build && cd build && cmake -DCMAKE_BUILD_TYPE=Debug .. && make)
  (cd example/fly_mission && mkdir build && cd build && cmake -DCMAKE_BUILD_TYPE=Debug .. && make)
  (cd example/offboard_velocity && mkdir build && cd build && cmake -DCMAKE_BUILD_TYPE=Debug .. && make)
  @@ -14,7 +14,7 @@ make clean
  make BUILD_TYPE=Release run_unit_tests -j4
  make install
  make docs
  -make fix-style
  +make fix_style
  (cd example/takeoff_land && mkdir build && cd build && cmake -DCMAKE_BUILD_TYPE=Release .. && make)
  (cd example/fly_mission && mkdir build && cd build && cmake -DCMAKE_BUILD_TYPE=Release .. && make)
  (cd example/offboard_velocity && mkdir build && cd build && cmake -DCMAKE_BUILD_TYPE=Release .. && make)
  