[docs] minor cleanup of the docs/ directory

Change-Id: Ic9d0805ee7658b97b3075dd129d4fb471bff3ccd
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/336560
Commit-Queue: Nate Bosch <nbosch@google.com>
Auto-Submit: Devon Carew <devoncarew@google.com>
Reviewed-by: Nate Bosch <nbosch@google.com>

docs/process/language-versions-and-experiments.md

@@ -261,7 +261,7 @@ use `?` and `late` in their library today.
 
     ```yaml
     environment:
-      sdk: >=2.8.0-dev.0 <2.8.0
+      sdk: '>=2.8.0-dev.0 <2.8.0'
     ```
 
     *SDK min constraint:* You can require a higher dev release if you want. The