Fix UnicodeString::fromCodePoints example

Author: jdreesen

components/string.rst

@@ -125,7 +125,7 @@ There are also some specialized constructors::
     $foo = ByteString::fromRandom(12);
 
     // CodePointString and UnicodeString can create a string from code points
-    $foo = UnicodeString::fromCodePoints(0x928, 0x92E, 0x938, 0x94D, 0x924, 0x947);
+    $foo = (string) UnicodeString::fromCodePoints(0x928, 0x92E, 0x938, 0x94D, 0x924, 0x947);
     // $foo = 'नमस्ते'
 
 Methods to Transform String Objects