Fix typo in FieldArray example (#447)

Surely no one would just copy a code sample and paste it into their production application.......

BUT just in case, this should fix a syntax error that they might encounter. 🙈

README.md

@@ -1331,13 +1331,13 @@ export const FriendList = () => (
                     <Field name={`friends.${index}`} />
                     <button
                       type="button"
-                      onClick={() => arrayHelpers.remove(index) // remove a friend from the list}
+                      onClick={() => arrayHelpers.remove(index)} // remove a friend from the list
                     >
                       -
                     </button>
                     <button
                       type="button"
-                      onClick={() => arrayHelpers.insert(index, '') // insert an empty string at a position}
+                      onClick={() => arrayHelpers.insert(index, '')} // insert an empty string at a position
                     >
                       +
                     </button>
@@ -1348,7 +1348,7 @@ export const FriendList = () => (
                   type="button"
                   onClick={() => arrayHelpers.push('')}
                 >
-                  {/** show this when user has removed all friends from the list */}
+                  {/* show this when user has removed all friends from the list */}
                   Add a friend
                 </button>
               )}