move optional dependencies to optional peer dependencies

see yarnpkg/rfcs#105

Author: stekycz

package.json

@@ -17,19 +17,17 @@
     "node": ">=8.10.0"
   },
   "peerDependencies": {
+    "@cookielab.io/eslint-plugin-custom-rules": "optional:^0.3.0",
+    "@typescript-eslint/eslint-plugin": "optional:^2.7.0",
+    "@typescript-eslint/parser": "optional:^2.7.0",
+    "babel-eslint": "optional:^10.0.3",
     "eslint": "^6.5.1",
+    "eslint-import-resolver-typescript": "optional:^2.0.0",
     "eslint-plugin-filenames": "^1.3.2",
-    "eslint-plugin-import": "^2.18.2"
-  },
-  "optionalDependencies": {
-    "@cookielab.io/eslint-plugin-custom-rules": "^0.3.0",
-    "@typescript-eslint/eslint-plugin": "^2.7.0",
-    "@typescript-eslint/parser": "^2.7.0",
-    "babel-eslint": "^10.0.3",
-    "eslint-import-resolver-typescript": "^2.0.0",
-    "eslint-plugin-flowtype": "^4.4.1",
-    "eslint-plugin-sort-imports-es6-autofix": "^0.5.0",
-    "typescript": "^3.7.2"
+    "eslint-plugin-flowtype": "optional:^4.4.1",
+    "eslint-plugin-import": "^2.18.2",
+    "eslint-plugin-sort-imports-es6-autofix": "optional:^0.5.0",
+    "typescript": "optional:^3.7.2"
   },
   "devDependencies": {
     "@cookielab.io/eslint-plugin-custom-rules": "0.3.0",