Add file extensions to go_template lexer (#875)

Author: silverwind

lexers/embedded/go_template.xml

@@ -2,6 +2,8 @@
   <config>
     <name>Go Template</name>
     <alias>go-template</alias>
+    <filename>*.gotmpl</filename>
+    <filename>*.go.tmpl</filename>
   </config>
   <rules>
     <state name="template">
@@ -109,4 +111,4 @@
       </rule>
     </state>
   </rules>
-</lexer>
+</lexer>