treewide: add stephen-huan as maintainer

pkgs/applications/networking/sync/backintime/common.nix

···
     homepage = "https://github.com/bit-team/backintime";
     description = "Simple backup tool for Linux";
     license = lib.licenses.gpl2;
-    maintainers = [ ];
+    maintainers = with lib.maintainers; [ stephen-huan ];
     platforms = lib.platforms.all;
     longDescription = ''
       Back In Time is a simple backup tool (on top of rsync) for Linux

pkgs/development/libraries/science/math/blis/default.nix

···
     description = "BLAS-compatible linear algebra library";
     homepage = "https://github.com/flame/blis";
     license = licenses.bsd3;
-    maintainers = [ ];
+    maintainers = with maintainers; [ stephen-huan ];
     platforms = [ "x86_64-linux" ];
   };
 }