Remove Node.js v10 from test rotation.

The `@wry/*` packages are all believed to work in Node 10, but that
Node.js version has been end-of-life'd (even for security updates) since
April 2021: https://endoflife.date/nodejs

Removing v10 should fix the tests in PR #230, which are broken because
Node 10 does not understand class property syntax in the `tests.cjs.js`
bundle.

The main `@wry/equality` library continues to be compiled to es2015,
eliminating class syntax, but the tests need to be compiled to esnext to
test generator and async function equality.

There may be a way to satisfy both of these constraints, but the easiest
solution right now is to avoid testing in Node 10.

Author: benjamn

.github/workflows/main.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        node_version: ['10', '12', '14', '15', '16']
+        node_version: ['12', '14', '15', '16']
         os: [ubuntu-latest]
 
     steps: