hello-world.md: Change username to GitHub handle.

abhijeetc66 · alenavolk · commit 91b4cbac7078 · 2018-01-11T09:54:39.000-05:00
diff --git a/submit-a-pull-request/abhijeetc66/hello-world.md b/submit-a-pull-request/abhijeetc66/hello-world.md
@@ -1,2 +1,2 @@
 Hello world
-I am username. :tada:
+I am abhijeetc66. :tada:
