Update competitest plugin to insert problem url

This is the second time I'm doing this, I'm an idiot who
didn't pushed last time!

lua/plugins/competitest.lua

@@ -7,6 +7,7 @@ return {
         --     c = "~/.config/nvim/templates/template.c"
         -- }
         template_file = "~/.config/nvim/templates/template.$(FEXT)",
+        evaluate_template_modifiers = true,
         received_contests_directory = "/tmp/Competitive Programming/$(JUDGE)/$(CONTEST)",
         received_problems_path = function(task, extension)
             local hyphen = string.find(task.group, " %- ")

templates/template.c

@@ -1,3 +1,5 @@
+/* Problem URL: $(URL) */
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <math.h>

templates/template.cpp

@@ -1,3 +1,5 @@
+/* Problem URL: $(URL) */
+
 #include <bits/stdc++.h>
 
 using namespace std;