Fixed M2M100 test (following language code special character registration)
//!
//! let device = Device::cuda_if_available();
//! let mut vs = nn::VarStore::new(device);
-//! let tokenizer: M2M100Tokenizer = M2M100Tokenizer::from_file(
+//! let tokenizer: M2M100Tokenizer = M2M100Tokenizer::from_files(
//! vocab_path.to_str().unwrap(),
//! merges_path.to_str().unwrap(),
//! false,
