Update 'ORT_VERSION' to 1.8.1

Author: nbigaouette

README.md

@@ -7,7 +7,7 @@
 [![codecov](https://codecov.io/gh/nbigaouette/onnxruntime-rs/branch/master/graph/badge.svg)](https://codecov.io/gh/nbigaouette/onnxruntime-rs)
 
 This is an attempt at a Rust wrapper for
-[Microsoft's ONNX Runtime](https://github.com/microsoft/onnxruntime) (version 1.7).
+[Microsoft's ONNX Runtime](https://github.com/microsoft/onnxruntime) (version 1.8).
 
 This project consist on two crates:
 

onnxruntime-sys/build.rs

@@ -11,7 +11,7 @@ use std::{
 /// WARNING: If version is changed, bindings for all platforms will have to be re-generated.
 ///          To do so, run this:
 ///              cargo build --package onnxruntime-sys --features generate-bindings
-const ORT_VERSION: &str = "1.7.0";
+const ORT_VERSION: &str = "1.8.1";
 
 /// Base Url from which to download pre-built releases/
 const ORT_RELEASE_BASE_URL: &str = "https://github.com/microsoft/onnxruntime/releases/download";