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

chmuhammadsohaib · jajodiaraghav · commit 190e453bdb28 · 2018-01-07T02:46:21.000+05:30
diff --git a/submit-a-pull-request/chmuhammadsohaib/hello-world.md b/submit-a-pull-request/chmuhammadsohaib/hello-world.md
@@ -1,2 +1,2 @@
 Hello world
-I am username. :tada:
+I am chmuhammadsohaib. :tada:
