Update cloud build args (#4954)

flutter_image_build.yaml

diff --git a/flutter_image_build.yaml b/flutter_image_build.yaml
index bc6ffdb..8314963 100644
--- a/flutter_image_build.yaml
+++ b/flutter_image_build.yaml
@@ -2,7 +2,13 @@
 
 steps:
   - name: 'us-docker.pkg.dev/cloud-builders/ga/v1/docker'
-    args: ['build', '-t', 'us-docker.pkg.dev/$PROJECT_ID/flutter/flutter', 'Dockerfile.flutter']
+    args: 
+      - 'build'
+      - '-t'
+      - 'us-docker.pkg.dev/$PROJECT_ID/flutter/flutter'
+      - '-f'
+      - 'Dockerfile.flutter'
+      - '.'
 
 timeout: 1200s