Merge pull request #987 from nojaf/bump-fsdocs

Bump fsdocs-tool to v20 alpha 13

Author: nojaf

.config/dotnet-tools.json

@@ -3,7 +3,7 @@
   "isRoot": true,
   "tools": {
     "fsdocs-tool": {
-      "version": "20.0.0-alpha-009",
+      "version": "20.0.0-alpha-013",
       "commands": [
         "fsdocs"
       ]