doc: change ./node to node in debugger.md

Fixes: https://github.com/nodejs/node/issues/8942
PR-URL: https://github.com/nodejs/node/pull/8943
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

doc/api/debugger.md

@@ -120,7 +120,7 @@ It is also possible to set a breakpoint in a file (module) that
 isn't loaded yet:
 
 ```txt
-$ ./node debug test/fixtures/break-in-module/main.js
+$ node debug test/fixtures/break-in-module/main.js
 < debugger listening on port 5858
 connecting to port 5858... ok
 break in test/fixtures/break-in-module/main.js:1