Use .cjs extension

package.json

@@ -4,15 +4,15 @@
   "description": "Utility functions for working with Quadbins",
   "license": "MIT",
   "type": "module",
-  "main": "dist/cjs/index.js",
+  "main": "dist/cjs/index.cjs",
   "module": "dist/esm/index.js",
   "umd:main": "dist/umd/index.js",
   "types": "dist/types/index.d.ts",
   "exports": {
     ".": {
       "types": "./dist/types/index.d.ts",
       "import": "./dist/esm/index.js",
-      "require": "./dist/cjs/index.js"
+      "require": "./dist/cjs/index.cjs"
     },
     "./*": "./*"
   },
@@ -28,7 +28,7 @@
   "scripts": {
     "clean": "rm -rf dist/*",
     "build": "yarn clean && yarn build:cjs && yarn build:esm && yarn build:types && yarn build:umd",
-    "build:cjs": "tsc -p tsconfig/tsconfig.cjs.json",
+    "build:cjs": "tsc -p tsconfig/tsconfig.cjs.json && mv dist/cjs/index.js dist/cjs/index.cjs",
     "build:esm": "tsc -p tsconfig/tsconfig.esm.json",
     "build:types": "tsc -p tsconfig/tsconfig.types.json",
     "build:umd": "webpack --config tsconfig/webpack.config.cjs",