fix: add postcss dependency to fix build error (#606)

* fix: add postcss dependency to fix build error

* chore(contrib): add node about java dep for builds

Co-authored-by: Sherwin Heydarbeygi <[email protected]>

Author: luqven

CONTRIBUTING.md

@@ -154,6 +154,8 @@ To install all development dependencies, in the project's root directory, run
 npm install
 ```
 
+**Please note: the build process assumes Java is installed locally.**
+
 Once you're configured, building the JavaScript from the command line is easy:
 
 ```

package.json

@@ -82,7 +82,8 @@
     "webpack": "4.46.0",
     "webpack-cli": "4.3.1",
     "webpack-closure-compiler": "2.1.6",
-    "yargs": "16.2.0"
+    "yargs": "16.2.0",
+    "postcss": "^8.1.0"
   },
   "dependencies": {},
   "browserslist": [