ci(dockerfile): Move the gitbook:install step after the guide files a…

…re copied into the Docker image

Dockerfile

@@ -25,15 +25,15 @@ COPY .npmrc package.json yarn.lock ./
 # Install dependencies.
 RUN set -ex && \
     yarn install --pure-lockfile && \
-    yarn cache clean && \
-    yarn gitbook:install
+    yarn cache clean
 
 # Copy all source and test files into the working directory.
 # We use a .dockerignore file to prevent unnecessary or large files from being inadvertently copied.
 COPY . /app
 
 # Build the app.
 RUN yarn run build-package && \
+    yarn gitbook:install && \
     STYLEGUIDIST_ENV=staging yarn run build:docs-staging && \
     STYLEGUIDIST_ENV=production yarn run build-styleguide