Do not run test_string_substring if no_object.

README.md

@@ -317,8 +317,6 @@ Use `Engine::new_raw` to create a _raw_ `Engine`, in which:
 let mut engine = Engine::new_raw();             // create a 'raw' Engine
 
 engine.register_stdlib();                       // register the standard library manually
-
-engine.
 ```
 
 Evaluate expressions only

tests/string.rs

@@ -35,6 +35,7 @@ fn test_string() -> Result<(), EvalAltResult> {
 }
 
 #[cfg(not(feature = "no_stdlib"))]
+#[cfg(not(feature = "no_object"))]
 #[test]
 fn test_string_substring() -> Result<(), EvalAltResult> {
     let engine = Engine::new();