chore(poetry): Update deprecated key in dependency

Author: nebbles

pyproject.toml

@@ -27,7 +27,7 @@ requests = "^2.22"
 pyperclip = "^1.7"
 
 [tool.poetry.dev-dependencies]
-black = {version = "^18.3-alpha.0", allows-prereleases = true}
+black = {version = "^18.3-alpha.0", allow-prereleases = true}
 
 [build-system]
 requires = ["poetry>=0.12"]