message: fixed flag for javascript
  javascript flag does not work in the 1.6 flatc.exe, changed to --js
diff: @@ -29,7 +29,7 @@ For any schema input files, one or more generators can be specified:
  - `--python`, `-p`: Generate Python code.
  -- `--javascript`, `-s`: Generate JavaScript code.
  +- `--js`, `-s`: Generate JavaScript code.
  - `--php`: Generate PHP code.
  