[Fix] Fixes version array and changes it to a const.

lib/string.js

@@ -306,7 +306,7 @@ internals.String = class extends Any {
             'uuidv5': '5'
         };
 
-        let versions;
+        const versions = [];
 
         if (guidOptions && guidOptions.version) {
             if (!Array.isArray(guidOptions.version)) {
@@ -315,17 +315,14 @@ internals.String = class extends Any {
 
             Hoek.assert(guidOptions.version.length >= 1, 'version must have at least 1 valid version specified');
 
-            versions = [];
             for (let i = 0; i < guidOptions.version.length; ++i) {
                 let version = guidOptions.version[i];
                 Hoek.assert(typeof version === 'string', 'version at position ' + i + ' must be a string');
                 version = version.toLowerCase();
                 Hoek.assert(uuids[version], 'version at position ' + i + ' must be one of ' + Object.keys(uuids).join(', '));
+                Hoek.assert(versions.indexOf(version) === -1, 'version at position ' + i + ' must not be a duplicate');
                 versions.push(version);
             }
-
-            // Make sure we have a set of versions
-            versions = Hoek.unique(versions);
         }
 
         const regex = /^([\[{\(]?)([0-9A-F]{8})([:-]?)([0-9A-F]{4})([:-]?)([0-9A-F]{4})([:-]?)([0-9A-F]{4})([:-]?)([0-9A-F]{12})([\]}\)]?)$/i;