cookiecutter: fixed wrong key name for short_description

Author: deeenes

cookiecutter.json

@@ -2,7 +2,7 @@
     "project_name": "Project Name",
     "project_slug": "{{ cookiecutter.project_name|lower|replace(' ', '-') }}",
     "package_name": "{{ cookiecutter.project_slug|lower|replace('-', '_') }}",
-    "project_description": "A great new project",
+    "short_description": "A great new project",
     "author_full_name": "Your Name",
     "author_email": "your@email",
     "github_organization": "saezlab",