[Bug] Remove specific pipenv version restriction

[TimidRobot]

Description

PR #201 added a specific version of pipenv (2021.5.29). This was required as the current version of pipenv (2021.11.5.post0) does not work well on Ubuntu 20.04, which is the current default for GitHub Actions.

Reproduction

See pypa/pipenv#4833 and PR #201 GitHub Action logs.

Expectation

We should be able to use the latest version of pipenv (once it is not broken).

Once pipenv has been fixed, the specific version should be removed:

--- .github/workflows/pre-commit.yml
+++ .github/workflows/pre-commit.yml
@@ -61,12 +61,9 @@ jobs:
         python-version: "3.7"
 
     - name: Install pipenv
-      # Use pipenv 2021.5.29 to circumvent errors with 2021.11.5.post0 on
-      # Ubuntu 20.04
-      # https://github.com/pypa/pipenv/issues/4833
       run: |
         python -m pip install --upgrade pip
-        python -m pip install pipenv==2021.5.29
+        python -m pip install pipenv
 
     - name: Install Python dependencies
       run: |

Environment

• Ubuntu 20.04.3 LTS (Focal Fossa)
• Ubuntu-latest workflows will use Ubuntu-20.04 actions/runner-images#1816

Additional context

• Transifex push (code) #201
• 2021.11.5.post0, ubuntu 20.04: pipenv broken pypa/pipenv#4833