Improve grammar

Signed-off-by: Graham <gpe@openrs2.org>

archive/src/main/resources/org/openrs2/archive/templates/index.html

@@ -19,7 +19,7 @@
 				<p>
 					The archive uses content-addressable storage, converting
 					caches to the client's native
-					<code>.dat2</code>/<code>.idx</code> format on-demand. This
+					<code>.dat2</code>/<code>.idx</code> format on demand. This
 					provides several benefits: the disk space required to store
 					all available caches is reduced, and groups or XTEA keys
 					missing from one copy of the cache can be sourced