Bump docfx from 2.78.3 to 2.78.4 (#147)

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.config/dotnet-tools.json

@@ -17,7 +17,7 @@
       "rollForward": false
     },
     "docfx": {
-      "version": "2.78.3",
+      "version": "2.78.4",
       "commands": [
         "docfx"
       ],