Copy index.json in build script, not npm script

Move the duplication of the index.json file in the build.sh script instead of
the npm build-index script. This makes things cleaner.

scripts/build.sh

@@ -13,6 +13,7 @@ function initialize {
 
 function build_index {
   npm run build-index
+  cp index.json pages/
   echo "Pages index succesfully built."
 }