feat(terms): Simplify terms query generation

This doesn't change the output at all, but makes the code simpler

lib/leaf/terms.js

@@ -2,11 +2,12 @@ module.exports = function( property, value ){
   if( !property || !value) {
     return null;
   }
-  var query = {
-    terms:{}
-  };
 
-  query.terms[property] = value;
+  const query = {
+    terms: {
+      [property]: value
+    }
+  };
 
   return query;
 };