_content/doc/tutorial: fix mixup between "module" and "workspace"

The word "workspace" was intended to be used.

Fixes golang/go#67740

Change-Id: I942f3301eaaf8f3fc6eb8964d3ebe90503bdbc60
Reviewed-on: https://go-review.googlesource.com/c/website/+/590043
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Sam Thanawalla <samthanawalla@google.com>

_content/doc/tutorial/workspaces.md

@@ -187,7 +187,7 @@ We'll then add a new function to the `reverse` package that we can use instead o
    )
    ```
 
-   The module now includes both the `example.com/hello` module and the `golang.org/x/example/hello` module,
+   The workspace now includes both the `example.com/hello` module and the `golang.org/x/example/hello` module,
    which provides the `golang.org/x/example/hello/reverse` package.
 
    This will allow us to use the new code we will write in our copy of the `reverse` package