Use SPDX license identifier (#9)

https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license-and-license-files

Author: cdce8p

pyproject.toml

@@ -8,7 +8,7 @@ authors = [
     { name = "Manuel Stahl" },
     { name = "Martin Fuchs" },
 ]
-license = { file = "LICENSE" }
+license = "MIT"
 keywords = ["stiebel-eltron", "tecalor", "modbus"]
 classifiers = [
     "Programming Language :: Python :: 3.10",
@@ -22,7 +22,7 @@ dependencies = [
 ]
 
 [build-system]
-requires = ["hatchling"]
+requires = ["hatchling>=1.27.0"]
 build-backend = "hatchling.build"
 
 [project.optional-dependencies]