update parcel so it actually works and doesn't crash

but still use postcss because otherwise blueprint.js doesn't compile

frontend/.parcelrc

@@ -0,0 +1,16 @@
+{
+    "extends": "@parcel/config-default",
+    "transformers": {
+        "*.{ts,tsx}": [
+            "@parcel/transformer-typescript-tsc"
+        ],
+        "*.css": [
+            "@parcel/transformer-postcss"
+        ]
+    },
+    "optimizers": {
+        "*.css": [
+            "@parcel/optimizer-cssnano"
+        ]
+    }
+}