message: flatbuffers.h: fix documentation warning
  Fixes following clang -Wdocumentation warning:
  ```
  flatbuffers.h:1762:17: error: parameter ']' not found in the function declaration [-Werror,-Wdocumentation]
  /// v A const reference to the `std::vector` of structs to
  ```
diff: @@ -1759,7 +1759,7 @@ class FlatBufferBuilder {
  /// `vector`.
  /// @tparam T The data type of the `std::vector` struct elements.
  /// @tparam S The data type of the `std::vector` native struct elements.
  - /// @param[in]] v A const reference to the `std::vector` of structs to
  + /// @param[in] v A const reference to the `std::vector` of structs to
  /// serialize into the buffer as a `vector`.
  /// @return Returns a typed `Offset` into the serialized data indicating
  /// where the vector is stored.
  