fix(drone): added pip install to load from cache

.drone.yml

@@ -19,6 +19,7 @@ steps:
   - name: Lint - pylint
     image: python
     commands:
+      - pip install -r requirements.txt
       - pylint wsgi.py app/*.py
     volumes:
       - name: pip_cache
@@ -27,6 +28,7 @@ steps:
   - name: Lint - flake8
     image: python
     commands:
+      - pip install -r requirements.txt
       - flake8 wsgi.py app/*.py
     volumes:
       - name: pip_cache
@@ -35,6 +37,7 @@ steps:
   - name: Security analysis with bandit
     image: python
     commands:
+      - pip install -r requirements.txt
       - bandit -r app/
     volumes:
       - name: pip_cache