Add own name to Catrobat credits page (#112)

Author: herbsee02

_data/contributors.json

@@ -3237,6 +3237,11 @@
       "firstname": "Markus",
       "lastname": "Doppelreiter",
       "github": "doppem15"
+    },
+    {
+      "firstname": "Herbert",
+      "lastname": "Seewann",
+      "github": "herbsee02"
     }
   ]
 }