be_<= does not work now. use be <= instead

With latest rspec, test fails as below

```
Failures:

  1) The ReportManager should shorten extremely long report filenames
     Failure/Error: filename.length.should be_<= 255
     NoMethodError:
       undefined method `<=' for #<RSpec::Matchers::BuiltIn::BePredicate:0x007fb975240de8>
     # ./spec/ci/reporter/report_manager_spec.rb:48:in `block (2 levels) in <top (required)>'
```