Fix linting and make it play nicely with venv

.gitignore

@@ -22,6 +22,7 @@ keys/
 
 # Virtualenv
 /env
+/venv
 
 
 *.sublime-project

Makefile

@@ -1,4 +1,5 @@
 SHELL=/bin/bash
+LINT_PATHS=stable_baselines3/ tests/ docs/conf.py setup.py
 
 pytest:
 	./scripts/run_tests.sh
@@ -9,9 +10,9 @@ type:
 lint:
 	# stop the build if there are Python syntax errors or undefined names
 	# see https://lintlyci.github.io/Flake8Rules/
-	flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
+	flake8 ${LINT_PATHS} --count --select=E9,F63,F7,F82 --show-source --statistics
 	# exit-zero treats all errors as warnings.
-	flake8 . --count --exit-zero --statistics
+	flake8 ${LINT_PATHS} --count --exit-zero --statistics
 
 doc:
 	cd docs && make html

docs/conf.py

@@ -19,7 +19,7 @@ from unittest.mock import MagicMock
 # We CANNOT enable 'sphinxcontrib.spelling' because ReadTheDocs.org does not support
 # PyEnchant.
 try:
-    import sphinxcontrib.spelling
+    import sphinxcontrib.spelling  # noqa: F401
     enable_spell_check = True
 except ImportError:
     enable_spell_check = False
@@ -129,6 +129,7 @@ html_logo = '_static/img/logo.png'
 def setup(app):
     app.add_stylesheet("css/baselines_theme.css")
 
+
 # Theme options are theme-specific and customize the look and feel of a theme
 # further.  For a list of options available for each theme, see the
 # documentation.