Restore version specifier for local dependencies.

It was initially removed because [RFC #2906][1] mentioned it is no
longer necessary and the version is inferred. However, the version that
was actually stabilized does not include this change. For more details
details, see the "Changes from RFC" section of the [Cargo issue][2].

[1]: rust-lang/rfcs#2906
[2]: rust-lang/cargo#8415

crates/fleetspeak/Cargo.toml

@@ -15,7 +15,7 @@ documentation = "https://docs.rs/fleetspeak"
 
 [dependencies]
 byteorder = { version = "1.4.3" }
-fleetspeak-proto = { path = "../fleetspeak-proto" }
+fleetspeak-proto = { path = "../fleetspeak-proto", version = "0.3.1" }
 lazy_static = { version = "1.4.0" }
 log = { version = "0.4.19" }
 protobuf = { workspace = true }