Update _config endpoint documentation to reflect new location

[flimzy]

No description provided.

[nickva]

@flimzy Another good fix. Thanks again!

This needs a bit of a fix with length of underline for some titles.
For example:

(pr/109) $ make
sphinx-build -b html -a -W -n -A local=1 -D latex_elements.papersize=a4 -d build/doctree src/ build/html
Running Sphinx v1.4.5
loading pickled environment... done
building [mo]: all of 0 po files
building [html]: all source files
updating environment: 0 added, 11 changed, 0 removed
reading sources... [100%] whatsnew/2.0

Warning, treated as error:
.../src/docs/src/api/server/configuration.rst:23: WARNING: Title underline too short.

``/_node/{node-name}/_config``
============

[flimzy]

This needs a bit of a fix with length of underline for some titles.

Fixed.

[nickva]

+1 Thank you, @flimzy !