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)

actions/runner-images#572

* `npm audit fix`.

* Fix yaml ?

* Pyarrow issue fixed: huggingface/datasets#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.yml

@@ -69,11 +69,11 @@ jobs:
           path: ~/.cargo/registry
           key: ${{ runner.os }}-cargo-registry-${{ hashFiles('**/Cargo.lock') }}
 
-          # - name: Cache Cargo Build Target
-          #   uses: actions/cache@v1
-          #   with:
-          #     path: ./bindings/python/target
-          #     key: ${{ runner.os }}-cargo-python-build-${{ hashFiles('**/Cargo.lock') }}
+      - name: Cache Cargo Build Target
+        uses: actions/cache@v1
+        with:
+          path: ./bindings/python/target
+          key: ${{ runner.os }}-cargo-python-build-${{ hashFiles('**/Cargo.lock') }}
 
       - name: Lint with RustFmt
         uses: actions-rs/cargo@v1