doc: remove unneeded ellipsis in header

The ellipsis in `All together` is not needed. I've had it on my list of
"small things to take care of when you get a chance" for a while. The
Microsoft Style Guide says to not use ellipses except in certain cases,
and that reminded me to do it. The day has arrived!

PR-URL: nodejs#41888
Reviewed-By: Derek Lewis <[email protected]>
Reviewed-By: Mohammed Keyvanzadeh <[email protected]>
Reviewed-By: Mestery <[email protected]>
Reviewed-By: Benjamin Gruenbaum <[email protected]>
Reviewed-By: Tobias Nießen <[email protected]>
Reviewed-By: Filip Skokan <[email protected]>

doc/api/modules.md

@@ -171,7 +171,7 @@ The `.mjs` extension is reserved for [ECMAScript Modules][] which cannot be
 loaded via `require()`. See [Determining module system][] section for more info
 regarding which files are parsed as ECMAScript modules.
 
-## All together...
+## All together
 
 <!-- type=misc -->