docs: Replace deprecated `--all` flag with `--workspace`

Signed-off-by: Sebastian Martinez <me@sebastinez.dev>

CONTRIBUTING.md

@@ -11,7 +11,7 @@ simple guidelines.
 
 Always check your code with the linter (`clippy`), by running:
 
-    $ cargo clippy --all --tests
+    $ cargo clippy --workspace --tests
 
 And make sure your code is formatted with, using:
 
@@ -23,14 +23,14 @@ Finally, ensure there is no trailing whitespace anywhere.
 
 Make sure all tests are passing with:
 
-    $ cargo test --all
+    $ cargo test --workspace
 
 ## Checking the docs
 
 If you make documentation changes, you may want to check whether there are any
 warnings or errors:
 
-    $ cargo doc --all --all-features
+    $ cargo doc --workspace --all-features
 
 ## Code style