doc: fix incorrect fs.readFileSync example output
This fixes an incorrect example in the documentation for calling
fs.readFileSync
on a directory. The example was presumably copied from
the documentation for fs.readFile
, which has an error argument in its
callback.
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
documentation is changed or added -
commit message follows commit guidelines