Readme.txt not getting updated

by

  1. Change the Stable tag value to your current plugin version 1.0
  2. Make a folder in tags with name 1.0.
  3. Copy your plugin files for version 1.0 in that folder with readme.txt and push it on SVN.
  4. Do the same whenever you release a new version.

Please note:
What you keep in your trunk is development version. And defining Stable tag in readme.txt mean current stable version which will be available for download from all tags.

FAQ | Validate readme.txt