fsspec 0.8.6 fails if pyarrow is not installed

[clowtown]

I believe this is caused by #503

python 3.6 which worked on 0.8.5, now fails on 0.8.6.
File ".tox/plf/lib/python3.6/site-packages/fsspec/spec.py", line 81, in <module> pa_version = get_package_version_without_import("pyarrow") File ".tox/plf/lib/python3.6/site-packages/fsspec/utils.py", line 428, in get_package_version_without_import return importlib_metadata.distribution(name).version File ".tox/plf/lib/python3.6/site-packages/importlib_metadata/__init__.py", line 558, in distribution return Distribution.from_name(distribution_name) File ".tox/plf/lib/python3.6/site-packages/importlib_metadata/__init__.py", line 215, in from_name raise PackageNotFoundError(name) importlib_metadata.PackageNotFoundError: No package metadata was found for pyarrow

Frozen requirements from failing run

behave==1.2.6 boto3==1.9.203 boto3-type-annotations==0.3.1 botocore==1.12.232 certifi==2020.12.5 chardet==3.0.4 Cython==0.29.22 dataclasses==0.7 Deprecated==1.2.11 docutils==0.15.2 fastparquet==0.4.1 fsspec==0.8.6 idna==2.8 importlib-metadata==1.7.0 importlib-resources==3.3.0 jmespath==0.10.0 JSON-minify==0.3.0 llvmlite==0.35.0 marshmallow==3.8.0 marshmallow-dataclass==8.0.0 marshmallow-enum==1.5.1 mypy-extensions==0.4.3 ndjson==0.3.1 numba==0.52.0 numpy==1.16.6 packaging==20.9 pandas==0.24.2 parse==1.19.0 parse-type==0.5.2 pyparsing==2.4.7 python-dateutil==2.8.1 python-snappy==0.5.4 pytz==2021.1 requests==2.22.0 requests-aws-sign==0.1.6 s3fs==0.4.2 s3transfer==0.2.1 six==1.15.0 tenacity==6.2.0 thrift==0.13.0 typeguard==2.10.0 typing-extensions==3.7.4.3 typing-inspect==0.6.0 urllib3==1.25.11 wrapt==1.12.1 zipp==3.4.0

[martindurant]

Fixing, will re-release. It seems that on some versions, you get an ImportError, which is what I would have expected.