Update mautrix-python and unpin yarl/aiohttp

requirements.txt

@@ -1,8 +1,8 @@
 ruamel.yaml>=0.15.35,<0.17
 python-magic>=0.4,<0.5
 commonmark>=0.8,<0.10
-aiohttp>=3,<3.7
-yarl>=1,<1.6
+aiohttp>=3,<4
+yarl>=1,<2
 attrs>=19.1
-mautrix==0.8.0rc1
+mautrix==0.8.0rc4
 asyncpg>=0.20,<0.22