* Build and publish wheels on GitHub Actions

* Remove Python 3.6

It has weird errors when importing

```
thread '<unnamed>' panicked at 'assertion failed: `(left != right)`
  left: `0`,
 right: `0`', C:\Users\runneradmin\.cargo\git\checkouts\pyo3-a22e69bc62b9f0fd\13cd092\src\gil.rs:83:13
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "C:\hostedtoolcache\windows\Python\3.6.8\x64\lib\site-packages\robyn\__init__.py", line 1, in <module>
    from .robyn import Server
pyo3_runtime.PanicException: assertion failed: `(left != right)`
  left: `0`,
 right: `0`
```