Incorrect code in string rotation

[alexrud-perf]

cracking-the-coding-interview/src/chapter01ArraysAndStrings/StringRotation.java

Line 15 in efe6d6c

return isSubstring((s1 + s2), s1);

current implementation always returns true, even if s2 contains all different characters: isRotation("abcd", "1234") -> true

it should be:

return isSubstring((s1 + s1), s2);