Doc: update examples

[Nugine]

rust-rocksdb/README.md

Lines 86 to 90 in e97c9b5

	let mut batch = WriteBatch::new(); // WriteBatch and db both have trait Writable
	batch.put(b"my key", b"my value");
	batch.put(b"key2", b"value2");
	batch.put(b"key3", b"value3");
	db.write(batch); // Atomically commits the batch

rust-rocksdb/src/rocksdb.rs

Lines 806 to 808 in e97c9b5

	pub fn write(&self, batch: &WriteBatch) -> Result<(), String> {
	self.write_opt(batch, &WriteOptions::new())
	}

Corrected:

db.write(&batch).unwrap();

[tabokie]

Thanks for the catch! Could you send us a PR to fix it?