added trim for string

src/Utils/Dbo/LuStringDbo.php

@@ -82,4 +82,9 @@ class LuStringDbo extends LuDbo
             throw new LuDboConstraintException("String length must be smaller or equal to ${max}");
         }
     }
+    
+    public function trim()
+    {
+        $this->_value = trim($this->_value);
+    }
 }