Remove exclamation mark from "String not found!"

Remove exclamation mark from "String not found!"

When using 'find' and a string is not found, this is not an error or a
surprising event. It is often expected (e.g. after searching through
the whole document for a certain string eventually you will get this
message). The exclamation mark should be reserved for messages that
are unexpected or that need extra attention, such as errors.