Fix caching errors during Firestore build

Author: schmidt-sebastian

packages/firestore/rollup.config.js

@@ -84,7 +84,6 @@ const browserPlugins = function () {
         }
       },
       cacheDir: tmp.dirSync(),
-      clean: true,
       abortOnError: false,
       transformers: [util.removeAssertAndPrefixInternalTransformer]
     }),

packages/firestore/test/unit/specs/describe_spec.ts

@@ -252,7 +252,7 @@ export function describeSpec(
     // Note: We use json-stable-stringify instead of JSON.stringify() to ensure
     // that the generated JSON does not produce diffs merely due to the order
     // of the keys in an object changing.
-    const output = stringify(specsInThisTest, {
+    const output = stringify.default(specsInThisTest, {
       space: 2,
       cmp: stringifyComparator
     });