Fix CI dependency install

Author: danielgtaylor

.github/workflows/ci.yml

@@ -11,7 +11,8 @@ jobs:
     - uses: actions/checkout@v1
     - name: Install dependencies
       run: |
-        sudo apt install protobuf-compiler pipenv
+        sudo apt install protobuf-compiler
+        pip install pipenv
         pipenv install --dev
     - name: Run tests
       run: |