Replace indexOf with includes (#6967)

* Replace `indexOf` with `includes`

* Add `unicorn/prefer-includes`

src/language-css/printer-postcss.js

@@ -118,7 +118,7 @@ function genericPrint(path, options, print) {
       const rawText = node.raws.text || node.text;
       // Workaround a bug where the location is off.
       // https://github.com/postcss/postcss-scss/issues/63
-      if (text.indexOf(rawText) === -1) {
+      if (!text.includes(rawText)) {
         if (node.raws.inline) {
           return concat(["// ", rawText]);
         }
@@ -512,7 +512,7 @@ function genericPrint(path, options, print) {
         // Ignore escape `\`
         if (
           iNode.value &&
-          iNode.value.indexOf("\\") !== -1 &&
+          iNode.value.includes("\\") &&
           iNextNode &&
           iNextNode.type !== "value-comment"
         ) {