Clippy fixes. (#846)

* Clippy fixes.

* Drop support for Python 3.6

* Remove other 3.6

* Re-enabling caches for build (5h + seems too long and issue seems
solved)

https://github.com/actions/virtual-environments/issues/572

* `npm audit fix`.

* Fix yaml ?

* Pyarrow issue fixed: https://github.com/huggingface/datasets/pull/2268

* Installing dev libraries.

* Install python dev elsewhere ?

* Typo.

* No sudo.

* ...

* Testing the GH again.

* Maybe v2 will fix ?

* Fixing tests on MacOS Python 3.8+

.github/workflows/python-release.yml

@@ -30,7 +30,7 @@ jobs:
     runs-on: windows-latest
     strategy:
       matrix:
-        python: [3.6, 3.7, 3.8, 3.9]
+        python: [3.7, 3.8, 3.9]
     steps:
       - name: Checkout repository
         uses: actions/checkout@v1
@@ -76,7 +76,7 @@ jobs:
     strategy:
       matrix:
         os: [windows-latest, macos-10.15]
-        python: [3.6, 3.7, 3.8, 3.9]
+        python: [3.7, 3.8, 3.9]
     steps:
       - name: Checkout repository
         uses: actions/checkout@v1