Update pre-commit hook URLs. (#9433)

Following up on #9412, this PR updates some pre-commit hook URLs that have moved. This now uses the canonical URLs instead of a redirect.

Note: As of PR #9412, the pre-commit configuration is used for style checks on CI. The versions used by pre-commit are in a separate virtual environment from any linters/formatters in the user's local/conda environment.

I also updated the pinned versions of `flake8`, `pydocstyle`, and `isort`, which are more than a year old. The updates to these hooks do not require any changes to the code for compliance, and I do not anticipate any PR conflicts. Users of pre-commit will be automatically upgraded next time pre-commit runs. I did not upgrade `black` or `mypy`:
- Upgrading `black` to the latest version introduces a relatively large number of small formatting changes and should be handled in a separate PR.
- Upgrading `mypy` to the latest version introduces an issue I reported in #9300 and should be handled in a separate PR.

Authors:
  - Bradley Dice (https://github.com/bdice)

Approvers:
  - Vyas Ramasubramani (https://github.com/vyasr)
  - Ashwin Srinath (https://github.com/shwina)

URL: #9433

.pre-commit-config.yaml

@@ -1,6 +1,6 @@
 repos:
-      - repo: https://github.com/pycqa/isort
-        rev: 5.6.4
+      - repo: https://github.com/PyCQA/isort
+        rev: 5.9.3
         hooks:
               - id: isort
                 alias: isort-cudf
@@ -27,13 +27,13 @@ repos:
                 name: isort-dask-cudf
                 args: ["--settings-path=python/dask_cudf/setup.cfg"]
                 files: python/dask_cudf/.*
-      - repo: https://github.com/ambv/black
+      - repo: https://github.com/psf/black
         rev: 19.10b0
         hooks:
               - id: black
                 files: python/.*
-      - repo: https://gitlab.com/pycqa/flake8
-        rev: 3.8.3
+      - repo: https://github.com/PyCQA/flake8
+        rev: 4.0.1
         hooks:
               - id: flake8
                 alias: flake8
@@ -65,8 +65,8 @@ repos:
               - id: mypy
                 args: ["--config-file=python/cudf/setup.cfg", "python/cudf/cudf"]
                 pass_filenames: false
-      - repo: https://github.com/pycqa/pydocstyle
-        rev: 6.0.0
+      - repo: https://github.com/PyCQA/pydocstyle
+        rev: 6.1.1
         hooks:
               - id: pydocstyle
                 args: ["--config=python/.flake8"]