chore: reorganize dependencies

package.json

@@ -8,12 +8,15 @@
   "dependencies": {
     "common-tags": "1.8.0",
     "cross-spawn": "6.0.5",
+    "postcss-load-config": "2.0.0",
+    "postcss-modules": "1.3.2",
     "style-inject": "0.3.0"
   },
+  "devDependencies": {
+    "postcss": "^7.0.2"
+  },
   "peerDependencies": {
-    "postcss": "^7.0.2",
-    "postcss-load-config": "^2.0.0",
-    "postcss-modules": "^1.3.2"
+    "postcss": "^7.0.2"
   },
   "keywords": [
     "postcss-runner",

yarn.lock

@@ -273,17 +273,17 @@ [email protected]:
     source-map "^0.5.6"
     supports-color "^3.2.3"
 
-postcss@7.0.2, postcss@^7.0.1:
-  version "7.0.2"
-  resolved "https://registry.yarnpkg.com/postcss/-/postcss-7.0.2.tgz#7b5a109de356804e27f95a960bef0e4d5bc9bb18"
+postcss@^6.0.1:
+  version "6.0.23"
+  resolved "https://registry.yarnpkg.com/postcss/-/postcss-6.0.23.tgz#61c82cc328ac60e677645f979054eb98bc0e3324"
   dependencies:
     chalk "^2.4.1"
     source-map "^0.6.1"
     supports-color "^5.4.0"
 
-postcss@^6.0.1:
-  version "6.0.23"
-  resolved "https://registry.yarnpkg.com/postcss/-/postcss-6.0.23.tgz#61c82cc328ac60e677645f979054eb98bc0e3324"
+postcss@^7.0.1, postcss@^7.0.2:
+  version "7.0.2"
+  resolved "https://registry.yarnpkg.com/postcss/-/postcss-7.0.2.tgz#7b5a109de356804e27f95a960bef0e4d5bc9bb18"
   dependencies:
     chalk "^2.4.1"
     source-map "^0.6.1"