message: Correct name of submodules in .gitmodules
  As per "name" is
  the name of the submodule. Hence this commit does make sure each
  submodule entry abides by it.
diff: -[submodule "libs/include/mavlink/v2.0"]
  +[submodule "c_library_v2"]
  path = third_party/mavlink/include/mavlink/v2.0
  url = https://github.com/mavlink/c_library_v2.git
  -[submodule "libs/gtest"]
  +[submodule "gtest"]
  path = third_party/gtest
  url = https://github.com/google/googletest
  [submodule "curl-android-ios"]
  path = core/third_party/curl-android-ios
  url = https://github.com/dronecore/curl-android-ios.git
  -[submodule "libs/tinyxml2"]
  +[submodule "tinyxml2"]
  path = core/third_party/tinyxml2
  url = https://github.com/leethomason/tinyxml2.git
  -[submodule "grpc/server/proto"]
  +[submodule "DronCore-Proto"]
  path = grpc/server/proto
  url = https://github.com/dronecore/DroneCore-Proto.git
  -[submodule "third_party/zlib"]
  +[submodule "zlib"]
  path = third_party/zlib
  url = https://github.com/madler/zlib
  ignore = dirty
  -[submodule "plugins/mission/third_party/json11"]
  +[submodule "json11"]
  path = plugins/mission/third_party/json11
  url = https://github.com/dropbox/json11
  