Revert "Update manifest.json"

This reverts commit f0bf95683741e5a0251a3d255d7edace78a6c147.
"Adds a back button to the UI"

First, minimal-ui takes up valueable screen space. We should value
the users screen space, and I believe users often install PWA's
_specifically_ to recover screen space taken by browser chrome[1]. I
know I do.

Second, devdocs already shows navigation arrows on mobile. A better
solution to a lack of back button (on desktop? where?) would be to
show those same navigation arrows there, rather than use minimal-ui.

Third, there's no rationale that I could find for this commit. No
explanation or issue linked. That's almost reason enough to revert.
Please write good commits: https://chris.beams.io/posts/git-commit/

[1] https://developer.mozilla.org/en-US/docs/Glossary/chrome

public/manifest.json

@@ -3,7 +3,7 @@
   "short_name": "DevDocs",
   "description": "API Documentation Browser",
   "start_url": "/",
-  "display": "minimal-ui",
+  "display": "standalone",
   "background_color": "#EEEEEE",
   "icons": [
     {