Update Cargo.toml files so docs.rs is happy (#492)

docs.rs is unhappy. I've updated the cargo-args so that it builds
correctly. Tested locally and it works with this change.

- [x] no changelog update needed

agb/Cargo.toml

@@ -24,6 +24,7 @@ rustc-hash = { version = "1", default-features = false }
 
 [package.metadata.docs.rs]
 default-target = "thumbv4t-none-eabi"
+cargo-args = ["-Zbuild-std=core,alloc"]
 
 [profile.dev]
 opt-level = 3

tracker/agb-tracker/Cargo.toml

@@ -27,3 +27,4 @@ debug = true
 
 [package.metadata.docs.rs]
 default-target = "thumbv4t-none-eabi"
+cargo-args = ["-Zbuild-std=core,alloc"]