examples/rust: Fix building of the hello world demo

When I renamed it from minimal to hello-world, it stopped being built
due to the make target name being the same as the directory name
(hello-world).

Rename the make target to rust-hello-world which also matches the naming
of the rest of the targets.

Fixes: 656c036 ("examples/rust: Add a minimal hello world rust example")
Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

Author: ac000

examples/rust/Makefile

@@ -2,7 +2,7 @@ include ../../shared.mk
 
 SDIR = examples/rust
 
-examples: rust-echo-request rust-upload-reflector hello-world
+examples: rust-echo-request rust-upload-reflector rust-hello-world
 
 rust-echo-request: echo-request/Cargo.toml echo-request/src/lib.rs
 	$(PP_GEN) $(SDIR)/echo-request/target/wasm32-wasi/
@@ -12,7 +12,7 @@ rust-upload-reflector: upload-reflector/Cargo.toml upload-reflector/src/lib.rs
 	$(PP_GEN) $(SDIR)/upload-reflector/target/wasm32-wasi/
 	$(v)cd upload-reflector; cargo build --target=wasm32-wasi
 
-hello-world: hello-world/Cargo.toml hello-world/src/lib.rs
+rust-hello-world: hello-world/Cargo.toml hello-world/src/lib.rs
 	$(PP_GEN) $(SDIR)/hello-world/target/wasm32-wasi/
 	$(v)cd hello-world; cargo build --target=wasm32-wasi