Fixed spelling and formatting for U.S. (#4289)

I believe this will fix the button near the bottom of https://momentjs.com. If not, feel free to delete this PR.

src/locale/es-us.js

@@ -1,5 +1,5 @@
 //! moment.js locale configuration
-//! locale : Spanish(United State) [es-us]
+//! locale : Spanish (United States) [es-us]
 //! author : bustta : https://github.com/bustta
 
 import moment from '../moment';