Update dependencies and setup.py classifiers

optional-requirements.txt

@@ -7,11 +7,11 @@ pycryptodome>=3,<4
 unpaddedbase64>=1,<2
 
 #/metrics
-prometheus_client>=0.6,<0.9
+prometheus_client>=0.6,<0.10
 
 #/formattednumbers
 phonenumbers>=8,<9
 
 #/qrlink
 qrcode>=6,<7
-Pillow>=4,<8
+Pillow>=4,<9

setup.py

@@ -59,6 +59,7 @@ setuptools.setup(
         "Programming Language :: Python :: 3",
         "Programming Language :: Python :: 3.7",
         "Programming Language :: Python :: 3.8",
+        "Programming Language :: Python :: 3.9",
     ],
     package_data={"mautrix_signal": [
         "example-config.yaml",