[Gallery] Fix directory structure

CONTRIBUTING.md

@@ -56,7 +56,7 @@ Each app should:
   [stable](https://github.com/flutter/flutter/wiki/Flutter-build-release-channels)
   release of the Flutter SDK.
 * Include the same
-  [`analysis_options.yaml`](https://github.com/flutter/samples/blob/master/gallery/gallery/analysis_options.yaml)
+  [`analysis_options.yaml`](https://github.com/flutter/samples/blob/master/gallery/analysis_options.yaml)
   file used throughout the repo. These files include a base set of analyzer
   conventions and lints.
 * Have no analyzer errors or warnings.

INDEX.md

@@ -139,7 +139,7 @@ thread and into an isolate.
 
 ## Demos
 
-#### [Shrine](gallery/gallery/lib/studies/shrine) _(Flutter team)_
+#### [Shrine](gallery/lib/studies/shrine) _(Flutter team)_
 The Shrine demo app from the Flutter team. It's designed to showcase how apps
 can put their own spin on the Material Design components and how to use
 ScopedModel to maintain app state across screens.

gallery/README.md

@@ -53,7 +53,7 @@ platform it runs on. This is determined based on window size as outlined in
 
 To generate localized strings or highlighted code segments, make sure that you
 have [grinder](https://pub.dev/packages/grinder) installed. You can install it
-by getting the packages in `samples/gallery/gallery/`:
+by getting the packages in `samples/gallery/`:
 ```
 flutter pub get
 ```