Update deps

PostCSS minor version bump
Svelte minor version bump
Rollup major update to version ^2.7
Note:
`@rollup/plugin-commonjs` was not updated due to issue with sapper:
sveltejs/sapper#1151

package.json

@@ -37,16 +37,16 @@
     "eslint-plugin-import": "^2.20.2",
     "eslint-plugin-svelte3": "^2.7.3",
     "npm-run-all": "^4.1.5",
-    "postcss": "^7.0.27",
+    "postcss": "^7.0.28",
     "postcss-import": "^12.0.1",
     "postcss-load-config": "^2.1.0",
     "postcss-preset-env": "^6.7.0",
-    "rollup": "^1.20.0",
+    "rollup": "^2.7.0",
     "rollup-plugin-babel": "^4.0.2",
     "rollup-plugin-svelte": "^5.0.1",
     "rollup-plugin-terser": "^5.3.0",
     "sapper": "^0.27.0",
-    "svelte": "^3.0.0",
+    "svelte": "^3.22.0",
     "svelte-preprocess": "^3.7.4",
     "tailwindcss": "^1.4.4"
   }