Fixes a typo on the govulncheck tutorial

Typo causes an extra code block to appear

Change-Id: I0912c53e5ca5aed1a6435d61db6c16b7de239d8b
Reviewed-on: https://go-review.googlesource.com/c/website/+/509375
Run-TryBot: Brandon Kessler <bkessler@google.com>
Reviewed-by: Julie Qiu <julieqiu@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

_content/doc/tutorial/govulncheck.md

@@ -81,7 +81,7 @@ the tag is undefined, or whether there was an error while parsing the tag.
 **Step 3.** Run `go mod tidy`, which will populate the `go.mod` file with all the
 dependencies required by the code you added to `main.go` in the previous step.
 
-    From the `vuln-tutorial` folder, run:
+From the `vuln-tutorial` folder, run:
 
 ```
 $ go mod tidy