C++14 is required for the example

[jun-shibata]

It's a small thing, but the compile option -std=c++11 in this example should be updated.

https://github.com/google/benchmark?tab=readme-ov-file#basic-usage

The error occurs because make_unique is used.

benchmark/include/benchmark/benchmark.h:1371:12: error: 'make_unique' is not a member of 'std'
 1371 |       std::make_unique<internal::FunctionBenchmark>(name, fn));

Please fix the compilation command.

# Example on linux after running the build steps above. Assumes the
# `benchmark` and `build` directories are under the current directory.
- $ g++ mybenchmark.cc -std=c++11 -isystem benchmark/include \
+ $ g++ mybenchmark.cc -std=c++14 -isystem benchmark/include \
  -Lbenchmark/build/src -lbenchmark -lpthread -o mybenchmark