Upgrade deps to enable postcss 8

package.json

@@ -1,6 +1,6 @@
 {
   "name": "rollup-plugin-postcss",
-  "version": "3.0.0",
+  "version": "3.1.8",
   "description": "Seamless integration between Rollup and PostCSS",
   "main": "dist/index.js",
   "files": [
@@ -35,18 +35,19 @@
   "devDependencies": {
     "@babel/core": "^7.9.0",
     "@babel/preset-env": "^7.9.5",
-    "autoprefixer": "^9.7.6",
+    "autoprefixer": "^10.0.1",
     "babel-core": "^7.0.0-bridge.0",
-    "babel-jest": "^25.3.0",
-    "bili": "^4.9.0",
+    "babel-jest": "^26.6.3",
+    "bili": "^5.0.5",
     "eslint-config-rem": "^4.0.0",
     "fs-extra": "^9.0.0",
-    "jest": "^25.3.0",
+    "jest": "^26.6.3",
     "less": "^3.11.1",
     "node-sass": "^4.13.1",
+    "postcss": "^8.1.6",
     "rollup": "^2.6.1",
     "stylus": "^0.54.7",
-    "sugarss": "^2.0.0",
+    "sugarss": "^3.0.3",
     "xo": "^0.29.1"
   },
   "dependencies": {
@@ -56,15 +57,17 @@
     "import-cwd": "^3.0.0",
     "p-queue": "^6.3.0",
     "pify": "^5.0.0",
-    "postcss": "^7.0.27",
-    "postcss-load-config": "^2.1.0",
-    "postcss-modules": "^2.0.0",
+    "postcss-load-config": "^3.0.0",
+    "postcss-modules": "^3.2.2",
     "promise.series": "^0.2.0",
     "resolve": "^1.16.1",
     "rollup-pluginutils": "^2.8.2",
     "safe-identifier": "^0.4.1",
     "style-inject": "^0.3.0"
   },
+  "peerDependencies": {
+    "postcss": "^8.1.6"
+  },
   "xo": {
     "extends": "rem",
     "envs": [