Fix package.json preinstall hook for busybox/docker build

package.json

@@ -133,6 +133,6 @@
     "build-hot": "NODE_ENV=hot webpack && NODE_ENV=hot webpack-dev-server",
     "start": "yarn run build && lein ring server",
     "storybook": "start-storybook -p 9001",
-    "preinstall": "ps -a | grep -v grep | grep -q yarn || (echo '\\033[0;33mSorry, npm is not supported. Please use Yarn (https://yarnpkg.com/).\\033[0m'; exit 1)"
+    "preinstall": "ps -fp $PPID | grep -q yarn || echo '\\033[0;33mSorry, npm is not supported. Please use Yarn (https://yarnpkg.com/).\\033[0m'"
   }
 }