Small `formatMatches` change for single results

This changes `formatMatches` to notify the user that they can
select the single result.  This is a more clear result compared to
the previous one.

This closes the following issue: https://github.com/ivaynberg/select2/issues/2329

select2.js

@@ -1110,7 +1110,7 @@ the specific language governing permissions and limitations under the Apache Lic
                     this.attachEvent("onpropertychange", self._sync);
                 });
             }
-            
+
             // safari, chrome, firefox, IE11
             observer = window.MutationObserver || window.WebKitMutationObserver|| window.MozMutationObserver;
             if (observer !== undefined) {
@@ -1349,7 +1349,7 @@ the specific language governing permissions and limitations under the Apache Lic
                 lastMousePosition.x = e.pageX;
                 lastMousePosition.y = e.pageY;
             });
-            
+
             return true;
         },
 
@@ -3397,7 +3397,7 @@ the specific language governing permissions and limitations under the Apache Lic
         },
         formatResultCssClass: function(data) {return data.css;},
         formatSelectionCssClass: function(data, container) {return undefined;},
-        formatMatches: function (matches) { return matches + " results are available, use up and down arrow keys to navigate."; },
+        formatMatches: function (matches) { if (matches === 1) { return "One result is available, press enter to select it."; } return matches + " results are available, use up and down arrow keys to navigate."; },
         formatNoMatches: function () { return "No matches found"; },
         formatInputTooShort: function (input, min) { var n = min - input.length; return "Please enter " + n + " or more character" + (n == 1? "" : "s"); },
         formatInputTooLong: function (input, max) { var n = input.length - max; return "Please delete " + n + " character" + (n == 1? "" : "s"); },

select2_locale_en.js.template

@@ -1,13 +1,13 @@
 /**
  * Select2 <Language> translation.
- * 
+ *
  * Author: Your Name <your@email>
  */
 (function ($) {
     "use strict";
 
     $.extend($.fn.select2.defaults, {
-        formatMatches: function (matches) { return matches + " results are available, use up and down arrow keys to navigate."; },
+        formatMatches: function (matches) { if (matches === 1) { return "One result is available, press enter to select it."; } return matches + " results are available, use up and down arrow keys to navigate."; },
         formatNoMatches: function () { return "No matches found"; },
         formatInputTooShort: function (input, min) { var n = min - input.length; return "Please enter " + n + " or more character" + (n == 1 ? "" : "s"); },
         formatInputTooLong: function (input, max) { var n = input.length - max; return "Please delete " + n + " character" + (n == 1 ? "" : "s"); },