docs: update .all-contributorsrc

Author: allcontributors[bot]

.all-contributorsrc

@@ -25,6 +25,15 @@
       "contributions": [
         "content"
       ]
+    },
+    {
+      "login": "tankala",
+      "name": "Tankala Ashok",
+      "avatar_url": "https://avatars.githubusercontent.com/u/29096822?v=4",
+      "profile": "http://tanka.la",
+      "contributions": [
+        "content"
+      ]
     }
   ]
 }