Change gunicorn to an optional dependency

poetry.lock

@@ -50,10 +50,10 @@ WTForms = "*"
 itsdangerous = "*"
 
 [[package]]
-category = "dev"
+category = "main"
 description = "WSGI HTTP Server for UNIX"
 name = "gunicorn"
-optional = false
+optional = true
 python-versions = ">=3.4"
 version = "20.0.4"
 
@@ -165,7 +165,7 @@ ipaddress = ["ipaddress"]
 locale = ["Babel (>=1.3)"]
 
 [metadata]
-content-hash = "5a3b077899ce6bd8f1a70c4fc48784486bb1373081d94c5b772191e7edb2788c"
+content-hash = "899cd435824d023104e5842da0f85bf3d82cf4a83137abfe19b7d817e1a12974"
 lock-version = "1.0"
 python-versions = "^3.8"
 

pyproject.toml

@@ -9,10 +9,10 @@ python = "^3.8"
 flask = "^1.1.2"
 flask-login = "^0.5.0"
 flask_wtf = "^0.14.3"
+gunicorn = {version = "^20.0.4", optional = true}
 
 [tool.poetry.dev-dependencies]
 mypy = "^0.800"
-gunicorn = "^20.0.4"
 
 [tool.poetry.scripts]
 redstring-check = "redstring.parser:main"