fix(storybook): chromatic requires build script (#2360)

Author: castastrophe

.gitignore

@@ -22,6 +22,7 @@ package-lock.json
 build-storybook.log
 
 # Chromatic
+chromatic.log
 chromatic-build-*.xml
 chromatic-diagnostics*.json
 

.storybook/package.json

@@ -6,6 +6,9 @@
   "author": "Adobe",
   "homepage": "https://opensource.adobe.com/spectrum-css/preview",
   "main": "main.js",
+  "scripts": {
+    "build": "storybook build --config-dir . --output-dir ./storybook-static"
+  },
   "dependencies": {
     "@adobe/spectrum-css-workflow-icons": "^1.5.4",
     "@spectrum-css/expressvars": "^3.0.9",