Fix comment type in ReactElement (facebook#12314)

Author: Gustavo Saiani

packages/react/src/ReactElement.js

@@ -109,7 +109,7 @@ function defineRefPropWarningGetter(props, displayName) {
  */
 const ReactElement = function(type, key, ref, self, source, owner, props) {
   const element = {
-    // This tag allow us to uniquely identify this as a React Element
+    // This tag allows us to uniquely identify this as a React Element
     $$typeof: REACT_ELEMENT_TYPE,
 
     // Built-in properties that belong on the element