message: travis-docker-build: use proper syntax to install
diff: set -e
  make BUILD_TYPE=Debug run_unit_tests -j4
  -make install
  +make default install
  make docs
  make fix_style
  (cd example/takeoff_land && mkdir build && cd build && cmake -DCMAKE_BUILD_TYPE=Debug .. && make)
  @@ -13,7 +13,7 @@ make clean
  git clean -dfx
  make BUILD_TYPE=Release run_unit_tests -j4
  -make install
  +make default install
  make docs
  make fix_style
  (cd example/takeoff_land && mkdir build && cd build && cmake -DCMAKE_BUILD_TYPE=Release .. && make)
  