Pretty-print common type names.

tests/decrement.rs

@@ -9,7 +9,7 @@ fn test_decrement() -> Result<(), EvalAltResult> {
     let r = engine.eval::<String>("let s = \"test\"; s -= \"ing\"; s");
 
     match r {
-        Err(EvalAltResult::ErrorFunctionNotFound(err, _)) if err.starts_with("- ") => (),
+        Err(EvalAltResult::ErrorFunctionNotFound(err, _)) if err == "- (string, string)" => (),
         _ => panic!(),
     }
 

tests/mismatched_op.rs

@@ -7,7 +7,7 @@ fn test_mismatched_op() {
     let r = engine.eval::<i64>("60 + \"hello\"");
 
     match r {
-        Err(EvalAltResult::ErrorMismatchOutputType(err, _)) if err == "alloc::string::String" => (),
+        Err(EvalAltResult::ErrorMismatchOutputType(err, _)) if err == "string" => (),
         _ => panic!(),
     }
 }