Add theme-ui to devDependencies

Author: Aleksandra Sikora

packages/style-guide/package.json

@@ -14,14 +14,17 @@
   "peerDependencies": {
     "@emotion/core": "^10.0.10",
     "react": "^16.8.6",
-    "theme-ui": "^0.3.0"
+    "theme-ui": "^0.4.0-alpha.1"
   },
   "dependencies": {
     "@theme-ui/presets": "^0.4.0-alpha.1",
     "color": "^3.1.2",
     "@types/color": "3.0.1",
     "lodash.get": "^4.4.2"
   },
+  "devDependencies": {
+    "theme-ui": "^0.4.0-alpha.1"
+  },
   "publishConfig": {
     "access": "public"
   },