fix: remove CPython 3.5 builds

support will be dropped when 3.5 reaches EOL

Author: standy66

.travis.yml

@@ -13,10 +13,6 @@ env:
   - PYTHON_IMAGE="pypy:3.6" PURERPC_BACKEND="asyncio"
   - PYTHON_IMAGE="pypy:3.6" PURERPC_BACKEND="curio"
   - PYTHON_IMAGE="pypy:3.6" PURERPC_BACKEND="trio"
-  - PYTHON_IMAGE="python:3.5" PURERPC_BACKEND="asyncio"
-  - PYTHON_IMAGE="python:3.5" PURERPC_BACKEND="uvloop"
-  - PYTHON_IMAGE="python:3.5" PURERPC_BACKEND="curio"
-  - PYTHON_IMAGE="python:3.5" PURERPC_BACKEND="trio"
   - PYTHON_IMAGE="python:3.6" PURERPC_BACKEND="asyncio"
   - PYTHON_IMAGE="python:3.6" PURERPC_BACKEND="uvloop"
   - PYTHON_IMAGE="python:3.6" PURERPC_BACKEND="curio"