Make rustdoc respect --error-format short

The other two (`human` and `json`) are already handled.

src/librustdoc/doctest.rs

@@ -296,7 +296,12 @@ fn run_test(
         }
     });
     if let ErrorOutputType::HumanReadable(kind) = options.error_format {
-        let (_, color_config) = kind.unzip();
+        let (short, color_config) = kind.unzip();
+
+        if short {
+            compiler.arg("--error-format").arg("short");
+        }
+
         match color_config {
             ColorConfig::Never => {
                 compiler.arg("--color").arg("never");