refactor(prelude): micro-optimisations

 - coverted `const` to `var` to reduce transformation time
 - change AssignmentExpression to UpdateExpression (less AST nodes)

Author: olegskl

src/templates/.eslintrc

@@ -8,6 +8,7 @@
   },
   "rules": {
     "no-unused-vars": "off",
-    "no-var": "off"
+    "no-var": "off",
+    "no-plusplus": "off"
   }
 }

src/templates/prelude.js

@@ -1,9 +1,9 @@
-const VARIABLE = (function (context) {
-  const locations = JSON.parse(LOCATIONS);
+var VARIABLE = (function (context) {
+  var locations = JSON.parse(LOCATIONS);
   context[NAMESPACE] = context[NAMESPACE] || {};
   context[NAMESPACE][FILEPATH] = locations;
   return function (id, value) {
-    locations[id][0] += 1;
+    locations[id][0]++;
     return value;
   };
 })(