Client: client does not close SSL socket after request completes

#### Environment details

1. Occurs with any request using googlemaps.Client
2. macOS Mojave
3. Library version: 4.4.2

#### Steps to reproduce

1. Instantiate a googlemaps Client
2. Make a request
3. Observe warning of unclosed SSL socket in console

#### Code example

```python
import googlemaps

def get_lat_lng(self, address: str):
gmaps = googlemaps.Client(key="api_key")
geocode_result = gmaps.geocode(address)
return geocode_result

```

#### Stack trace
```
ResourceWarning: unclosed
```

### Impact:
Services using the googlemaps client could easily run out of sockets because of this bug.

### Potential resolution:
This bug appears to be the same as https://github.com/googleapis/google-api-python-client/issues/618
If it is indeed the same there was a fix in google-api-python-client here: https://github.com/googleapis/google-api-python-client/pull/1038

從 googlemaps.Client 開始，沿著 geocode 請求路徑進行追蹤，然後使用程式碼範例重現 ResourceWarning。將請求清理行為與所參照的 google-api-python-client issue 和 pull request 進行比較；完成的標準是請求不再留下未關閉的 SSL socket。

由索引模型根據 Issue 內容生成。