[mod] oscar theme: added option into gruntfile.js for generate sourceMap

Credits go to @mrwormo  (see PR #2308 )

searx/static/themes/oscar/gruntfile.js

@@ -13,6 +13,7 @@ module.exports = function(grunt) {
     },
     uglify: {
       options: {
+        sourceMap: true,
         banner: '/*! oscar/searx.min.js | <%= grunt.template.today("dd-mm-yyyy") %> | <%= process.env.GIT_URL %>  */\n'
       },
       dist: {