Move non-obligatory dependencies to dev group

Move all but the obligatory dependencies to the `dev` group.  This
ensures that these packages (such as `pytest-cov`) are not incorrectly
installed into the production environment, e.g. when issuing
`pip install git+https://github.com/kakolukia/pypugjs`.

pyproject.toml

@@ -7,23 +7,21 @@ license = "MIT"
 
 [tool.poetry.dependencies]
 python = "^3.8"
-Jinja2 = "^3.1.1"
-Mako = "^1.1.3"
-tornado = "^6.0.4"
+charset-normalizer = "^2.1.0"
 six = "^1.15.0"
+
+[tool.poetry.group.dev.dependencies]
 coverage = "^6.3.2"
-Flask = "^2.1.1"
-charset-normalizer = "^2.1.0"
+Django = "^4.0.6"
 flake8 = "^4.0.1"
+Flask = "^2.1.1"
+icecream = "^2.1.3"
+Jinja2 = "^3.1.1"
+Mako = "^1.1.3"
 pytest = "^7.1.2"
 pytest-asyncio = "^0.19.0"
 pytest-cov = "^3.0.0"
-
-[tool.poetry.dev-dependencies]
-
-[tool.poetry.group.dev.dependencies]
-icecream = "^2.1.3"
-Django = "^4.0.6"
+tornado = "^6.0.4"
 
 [build-system]
 requires = ["poetry-core>=1.0.0"]