doc: use "Calls" over "Executes" for consistency

"Calls" is used frequently throughout the docs except for this line.
Use "Calls" over "Executes" to make it consistent.

PR-URL: https://github.com/nodejs/node/pull/2800


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>