Tests: Exclude some paths from PHPCS checks

We don't need to check things like the entire vendor folder and compiled assets so let's skip them in PHPCS.

.travis.yml

@@ -65,7 +65,7 @@ script:
     # -n flag: Do not print warnings. (shortcut for --warning-severity=0)
     # --standard: Use WordPress as the standard.
     # --extensions: Only sniff PHP files.
-    - if [[ "$SNIFF" == "1" ]]; then $PHPCS_DIR/bin/phpcs -p -s -v -n . --standard="WordPress-VIP-Go"; fi
+    - if [[ "$SNIFF" == "1" ]]; then $PHPCS_DIR/bin/phpcs -p -s -v -n . --standard="WordPress-VIP-Go" --ignore=assets/*,vendor/*,bin/*,node_modules/*; fi
     # Run unit tests
     - phpunit
     # Run linting