Bump MSRV to 1.70.0

The intention is to take advantage of `std::io::IsTerminal` that landed
in 1.70.0, both in `bat` and its dependencies (`clap`, `grep-cli`).

This will fix #2570 as well - `grep-cli` 0.1.9 has a patch for that.

Signed-off-by: mataha <mataha@users.noreply.github.com>

doc/README-zh.md

@@ -372,7 +372,7 @@ scoop install bat
 
 ### 从源码编译
 
-如果你想要自己构建`bat`，那么你需要安装有高于1.64.0版本的 Rust。
+如果你想要自己构建`bat`，那么你需要安装有高于1.70.0版本的 Rust。
 
 使用以下命令编译。