chore(deps): update dependency @rollup/plugin-babel to v6

Author: renovate[bot]

sapper/package-lock.json

@@ -30,7 +30,7 @@
     "@babel/plugin-transform-runtime": "7.12.1",
     "@babel/preset-env": "7.12.1",
     "@babel/runtime": "7.12.5",
-    "@rollup/plugin-babel": "5.2.1",
+    "@rollup/plugin-babel": "6.0.4",
     "@rollup/plugin-commonjs": "14.0.0",
     "@rollup/plugin-node-resolve": "8.4.0",
     "@rollup/plugin-replace": "2.3.4",