doc: remove unnecessary bind(this)

PR-URL: nodejs#4797
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Chris Dickinson <chris@neversaw.us>
Reviewed-By: Roman Reiss <me@silverwind.io>

doc/api/process.markdown

@@ -693,7 +693,7 @@ function MyThing(options) {
 
   process.nextTick(() => {
     this.startDoingStuff();
-  }.bind(this));
+  });
 }
 
 var thing = new MyThing();