Serve source map files as application/json

Developer tools don't actually care what `Content-Type` source map
files are served with. However, mapping their file extension (`.map`)
to the `application/json` media type, ensures that they will be served
compressed and their character encoding will be UTF-8.

See also:

* Source Map Revision 3 Proposal
  https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/

* Introduction to JavaScript Source Maps
  http://www.html5rocks.com/en/tutorials/developertools/sourcemaps/

* How CSS source maps work
  https://developers.google.com/chrome-developer-tools/docs/css-preprocessors#toc-how-css-source-maps-work

* What MIME-type should I use for source map files?
  http://stackoverflow.com/a/19912684

.htaccess

@@ -124,11 +124,13 @@ Options -MultiViews
     AddType audio/mp4                                   m4a f4a f4b
     AddType audio/ogg                                   oga ogg opus
 
+  # Data interchange
+    AddType application/json                            json map
+
   # JavaScript
     # Normalize to standard type (it's sniffed in IE anyways):
     # http://tools.ietf.org/html/rfc4329#section-7.2
     AddType application/javascript                      js
-    AddType application/json                            json
 
   # Video
     AddType video/mp4                                   f4v f4p m4v mp4

CHANGELOG.md

@@ -1,5 +1,6 @@
 ### HEAD
 
+* Serve source map files with the `application/json` Content-Type.
 * Make `RewriteCond`s for `example.com → www.example.com` more permissive
   ([#11](https://github.com/h5bp/server-configs-apache/issues/11)).
 * Add configs for Ogg Opus audio files