Fix the expected substring in ch11-01

[generalmimon]

According to Listing 11-9, the substring expected to be included is less than or equal to 100 (not Guess value must be less than or equal to 100 as written in the book, which is strictly speaking not the expected substring - it's almost the entire panic message except the final , got {}. part). See Listing 11-9:

    #[should_panic(expected = "less than or equal to 100")]

Also I think this was the only place in this chapter / in the book where I saw a string quotation in inline code additionally surrounded with single quotes ', so I removed them.

[generalmimon]

Actually, looking at the commit history, this discrepancy between the code and text probably exists since 34314c1, because the original expected substring was indeed Guess value must be less than or equal to 100:

listings/ch11-writing-automated-tests/listing-11-09/src/lib.rs:30-34

     #[test]
-    #[should_panic(expected = "Guess value must be less than or equal to 100")]
+    #[should_panic(expected = "less than or equal to 100")]
     fn greater_than_100() {
         Guess::new(200);
     }

[chriskrycho]

Ah, thank you!