chore: use same quotes everywhere (#169)

* chore: use same quotes everywhere
Use single quotes as in cssnano.
Previously the code used a mix of single and double quotes.

* chore: reformat with prettier

Author: ludofischer

package.json

@@ -28,22 +28,27 @@
   "repository": "https://github.com/postcss/postcss-calc.git",
   "eslintConfig": {
     "extends": [
-      "eslint:recommended"
+      "eslint:recommended",
+      "prettier"
     ],
     "env": {
       "node": true,
       "es2017": true
     },
-    "ignorePatterns": ["src/parser.js"],
+    "ignorePatterns": [
+      "src/parser.js"
+    ],
     "rules": {
       "curly": "error"
     }
   },
   "devDependencies": {
     "@types/node": "^17.0.14",
     "eslint": "^8.7.0",
+    "eslint-config-prettier": "^8.3.0",
     "jison-gho": "^0.6.1-216",
     "postcss": "^8.2.2",
+    "prettier": "^2.5.1",
     "typescript": "^4.5.5",
     "uvu": "^0.5.3"
   },