Regex octal escape sequence bug

While reading `lexer.coffee` spotted a hole in the `validateEscapes()` logic: if it encounters a valid "`INVALID_ESCAPE`" (eg `\1`) inside a regex interpolation-free section then it fails to check the rest of the section for actually invalid escapes. So eg `/\1\01/` should fail but instead generates `/\1\x001/`

Will submit a fixing pull request momentarily