Fix is_app check for generating app manifest.
Fix is_app check for generating app manifest.

cf-platform-eng/tile-generator,cf-platform-eng/tile-generator,alex-slynko/tile-generator,alex-slynko/tile-generator,cf-platform-eng/tile-generator,alex-slynko/tile-generator,alex-slynko/tile-generator,cf-platform-eng/tile-generator