fix incorrectly escaping ampersand

The bug is introduced in commit 175e04a862429903c17e5653e9fe1eda694354db, which quoted the URI. There is no need for escaping ampersand in quoted string, which only produces unwanted slash.

With some configuration:

```
location:North Pole
fetch_cmd:curl -vv
```

The output of curl shows the problem

```
> GET /data/2.5/weather?q=North%20Pole\&units=metric HTTP/1.1
```

For some unknown reason, city with one word results no error, only city names with space(s) have this issue.