Fix grammatical error

src/Monolog/Handler/StreamHandler.php

@@ -169,7 +169,7 @@ class StreamHandler extends AbstractProcessingHandler
             $status = mkdir($dir, 0777, true);
             restore_error_handler();
             if (false === $status && !is_dir($dir)) {
-                throw new \UnexpectedValueException(sprintf('There is no existing directory at "%s" and its not buildable: '.$this->errorMessage, $dir));
+                throw new \UnexpectedValueException(sprintf('There is no existing directory at "%s" and it could not be created: '.$this->errorMessage, $dir));
             }
         }
         $this->dirCreated = true;