treewide: remove periods from end of package descriptions

pkgs/development/python-modules/yamale/default.nix

@@ -30,7 +30,7 @@ buildPythonPackage rec {
   ];
 
   meta = with lib; {
-    description = "A schema and validator for YAML.";
+    description = "A schema and validator for YAML";
     homepage = "https://github.com/23andMe/Yamale";
     license = licenses.mit;
     maintainers = with maintainers; [ rtburns-jpl ];