fix: tokio-rs#942

Changes version numbers to start imports rather than the latest,
reducing the need make sure that the documentation numbers are always up
to date.

One downside is that the users must set an explicit the version number
before publishing their own crates.

README.md

@@ -30,9 +30,9 @@ First, add `prost` and its public dependencies to your `Cargo.toml`:
 
 ```ignore
 [dependencies]
-prost = "0.12"
+prost = "*"
 # Only necessary if using Protobuf well-known types:
-prost-types = "0.12"
+prost-types = "*"
 ```
 
 The recommended way to add `.proto` compilation to a Cargo project is to use the
@@ -380,9 +380,9 @@ the `std` features in `prost` and `prost-types`:
 
 ```ignore
 [dependencies]
-prost = { version = "0.6", default-features = false, features = ["prost-derive"] }
+prost = { version = "*", default-features = false, features = ["prost-derive"] }
 # Only necessary if using Protobuf well-known types:
-prost-types = { version = "0.6", default-features = false }
+prost-types = { version = "*", default-features = false }
 ```
 
 Additionally, configure `prost-build` to output `BTreeMap`s instead of `HashMap`s