Small typo (two articles) in the static file serving docs

[anonymous]

In the following sentence fragment, two articles are used, and only one should be used:

Django will still load templates with the older (no extension) name, but it will prefer a the directory_index.html version.

Instead, the latter half should say "but it will prefer the directory_index.html version" (removed 'a').

[Tim Graham]

typo

[Russell Keith-Magee]

(In [11535]) Fixed #11780 -- Corrected a typo in the static file serving docs.