help: update copyright

Author: raveit65

help/C/index.docbook

@@ -18,7 +18,7 @@
     <title>Image Viewer Manual</title>
 
     <copyright>
-      <year>2015</year>
+      <year>2019</year>
       <holder>MATE Documentation Project</holder>
     </copyright>
     <copyright> 
@@ -791,4 +791,4 @@
 	</variablelist>
   </section>
 </section>
-</article>
+</article>