Update requirements.

pyproject.toml

@@ -8,21 +8,22 @@ license = "MIT"
 
 [tool.poetry.dependencies]
 python = "^3.7.1"
-exact-cover = "1.0"
-numpy = "^1.20"
+exact-cover = "1.3.0"
 pretty-poly = "0.2.0"
 
 [tool.poetry.dev-dependencies]
 pytest = "^6.2.1"
 hypothesis = "^6.0.2"
 pytest-profiling = "^1.7.0"
 black = "^21.6b0"
-pytest-fail-slow = "^0.1.0"
 
 [tool.poetry.scripts]
 test = 'run_tests:run_tests'
 doctest = 'run_tests:run_doctests'
 
+[tool.poetry.group.dev.dependencies]
+pytest-fail-slow = ">=0.2.0,<0.3.0"
+
 [build-system]
 requires = ["poetry-core>=1.0.0"]
 build-backend = "poetry.core.masonry.api"