help: update copyright

Author: raveit65

help/C/index.docbook

@@ -20,7 +20,7 @@
         <title>Pluma Manual</title>
 
         <copyright its:translate="no">
-            <year>2015</year>
+            <year>2019</year>
             <holder>MATE Documentation Project</holder> 
         </copyright>
         <copyright its:translate="no">