Update to Terser 5.7 (#847)

* Update to Terser 5.7

* Create heavy-sheep-own.md

* Use npm@latest

Author: developit

.changeset/heavy-sheep-own.md

@@ -0,0 +1,5 @@
+---
+"microbundle": patch
+---
+
+- Upgrade to Terser [5.7](https://github.com/terser/terser/blob/master/CHANGELOG.md#v570) to re-enable support for `reduce_funcs:false` in `mangle.json` configuration.

.github/workflows/nodejs.yml

@@ -21,6 +21,8 @@ jobs:
         uses: actions/setup-node@v1
         with:
           node-version: ${{ matrix.node-version }}
+      - name: install npm@latest
+        run: npm i -g npm@latest --registry=https://registry.npmjs.org
       - name: npm install, build, and test
         run: |
           npm install