Dependency conflict between fairseq and hydra during installation

## 🐛 Bug There's a dependency conflict that causes and error during installation. When I run either of these commands `pip install --editable ./` and `CFLAGS="-stdlib=libc++" pip install --editable ./`, I see the following error from pip: `INFO: pip is looking at multiple versions of hydra-core to determine which version is compatible with other requirements. This could take a while. ERROR: Cannot install fairseq and fairseq==1.0.0a0+7bfcb50 because these package versions have conflicting dependencies. The conflict is caused by: fairseq 1.0.0a0+7bfcb50 depends on omegaconf<2.1 hydra-core 1.0.7 depends on omegaconf<2.1 and >=2.0.5 To fix this you could try to: 1. loosen the range of package versions you've specified 2. remove package versions to allow pip to attempt to solve the dependency conflict ERROR: ResolutionImpossible: for help visit https://pip.pypa.io/en/latest/topics/dependency-resolution/#dealing-with-dependency-conflicts ` This is on a freshly made virtual environment with `venv`.