Correct MIME for posts

Fixes #15

.htaccess

@@ -10,3 +10,9 @@ Options -Indexes
     RewriteRule ^(.*)$ index.php?path=$1 [QSA,L]
 </IfModule>
 
+<IfModule mod_rewrite.c>
+    # Make all /post/*.json served with correct MIME
+    RewriteEngine On
+    RewriteCond %{REQUEST_URI} ^/posts/
+    RewriteRule ^ - [T=application/activity+json]
+</IfModule>