Add override to LogStreamBuf::overflow()

[santigl]

This quiets warnings such as:

glog/logging.h:1122:20: 
error: ‘virtual std::basic_streambuf<char>::int_type google::base_logging::LogStreamBuf::overflow(std::basic_streambuf<char>::int_type)’ 
can be marked override [-Werror=suggest-override]
   virtual int_type overflow(int_type ch) {
                    ^~~~~~~~

[ukai]

lgtm.

need to fix https://github.com/google/glog/blob/master/src/windows/glog/logging.h#L1132 too?

[santigl]

Thank you, @ukai. I added the change for the Windows code.

[ukai]

why continuous-integration/travis-ci/pr doesn't report check status??

[sergiud]

Good question. Also, this change introduces a dependency to C++11 while glog still uses C++03. A possible workaround is to remove the virtual keyword instead of adding override.

[santigl]

why continuous-integration/travis-ci/pr doesn't report check status??

I hadn't notice it was missing a check before. The last push successfully triggered it.

[sergiud]

LGTM

[santigl]

Thanks, @sergiud. Feel free to merge this whenever you want.