Fix preview to not override page

Previously, sharedPageModel would override the specific page model. This
changes the order so that the specific page model is prioritized to
override the shared model.

Author: rwinch

gulp.d/tasks/build-preview-pages.js

@@ -50,7 +50,7 @@ module.exports =
                 const siteRootPath = path.relative(ospath.dirname(file.path), ospath.resolve(previewSrc))
                 const uiModel = { ...baseUiModel }
                 const sharedPageModel = page.component ? baseUiModel.shared[page.component.name][page.version] : {}
-                uiModel.page = { ...uiModel.page, ...page, ...sharedPageModel }
+                uiModel.page = { ...uiModel.page, ...sharedPageModel, ...page }
                 uiModel.siteRootPath = siteRootPath
                 uiModel.siteRootUrl = path.join(siteRootPath, 'index.html')
                 uiModel.uiRootPath = path.join(siteRootPath, '_')