doc: update 0022 to 0o022 in process.markdown

Per @cjihrig's suggestion

Author: jasnell

Diff for: doc/api/process.markdown

@@ -909,7 +909,7 @@ Sets or reads the process's file mode creation mask. Child processes inherit
 the mask from the parent process. Returns the old mask if `mask` argument is
 given, otherwise returns the current mask.
 
-    const newmask = 0022;
+    const newmask = 0o022;
     const oldmask = process.umask(newmask);
     console.log(
       `Changed umask from ${oldmask.toString(8)} to ${newmask.toString(8)}`