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

gcihelloworld · jajodiaraghav · commit c8fa407cb6dd · 2018-01-13T18:33:46.000+05:30
diff --git a/gcihelloworld/hello-world.md b/gcihelloworld/hello-world.md
@@ -1,2 +1,2 @@
 Hello world
-I am username. :tada:
+I am gcihelloworld. :tada:
