dont use ES6 syntax in grammar (#21)

* dont use ES6 syntax in grammar

In c8b9e2 we removed transpilation to ES5, which broke Charts e2e tests.

* Update grammar.pegjs

Co-Authored-By: Scott Sidwell <38820281+scottsidwell@users.noreply.github.com>

Co-authored-by: Scott Sidwell <38820281+scottsidwell@users.noreply.github.com>

packages/mongodb-language-model/grammar.pegjs

@@ -183,14 +183,17 @@ geometry_point
       distance:(
         value_separator quotation_mark operator:distance_operator quotation_mark
         name_separator value:number_positive
-        { return { [operator]: value }; }
+        { 
+          var result = {};
+          result[operator] = value;
+          return result;
+        }
       )*
     end_object
     {
-      return {
-        "$geometry": geometry,
-        ...(distance ? distance : {})
-      };
+      var result = distance || {};
+      distance.$geometry = geometry;
+      return result;
     }
 
 geometry_type