Skip build:lint if installed without source

package.json

@@ -46,7 +46,7 @@
     "env:yaml": "ts-node --project ./tsconfig.ts-node.json scripts/env-to-yaml.ts",
     "base-href": "ts-node --project ./tsconfig.ts-node.json scripts/base-href.ts",
     "check-circ-deps": "npx madge --exclude '(bitstream|bundle|collection|config-submission-form|eperson|item|version)\\.model\\.ts$' --circular --extensions ts ./",
-    "postinstall": "yarn build:lint"
+    "postinstall": "if [ -f lint/tsconfig.json ]; then yarn build:lint ; fi"
   },
   "browser": {
     "fs": false,