readme: switch Cargo.toml dependency version to "1"

Getting PRs to update this version when I invariably forget to update it
after a release is way too annoying. So just set it to "1".

README.md

@@ -29,7 +29,7 @@ Add this to your `Cargo.toml`:
 
 ```toml
 [dependencies]
-bstr = "1.0.1"
+bstr = "1"
 ```