Fix typos after i18n yml

app/views/admin/purchases/index.html.erb

@@ -6,7 +6,7 @@
 				<td><%= t(:title) %></td>
 				<td><%= t(:intro) %></td>
 				<td><%= t(:author) %></td>
-				<td><%= t(':action') %></td>
+				<td><%= t(:action) %></td>
 			</tr>
 		</thead>
 		<%# @purchases.each do |purchase| %>