Upgrade to standalone-single-spa-webpack-plugin@3 (single-spa#315)

Author: jolyndenning

Diff for: .changeset/happy-frogs-jump.md

@@ -0,0 +1,10 @@
+---
+"webpack-config-single-spa": major
+"webpack-config-single-spa-react": major
+"webpack-config-single-spa-react-ts": major
+"webpack-config-single-spa-ts": major
+---
+
+Upgrade to standalone-single-spa-webpack-plugin@3. For the majority of users, you can safely upgrade webpack-config-single-spa (-ts, -react, -react-ts) without any code changes.
+
+See https://github.com/single-spa/standalone-single-spa-webpack-plugin/releases/tag/v3.0.0 for details about what was changed. It only impacts running projects in standalone mode.