Allow to use different drivers in the same test suite

In my test suite I use different drivers, including appium_capybara.

I get this message for tests that use other drivers (selenium for example)
```
NoMethodError: undefined method `browser_initialized?' for #<Capybara::Selenium::Driver:0x007fdcf1773028>
appium_capybara/lib/appium_capybara/ext/session_ext.rb:5:in `reset!'
```

This pull request fix it
That's because `=` takes precedence over `and`, add parenthesis to prove it
```
a = (true and false); a
=> false
```

On the other hand, `and` takes precedence over `if`
```
 if true and false; 'yes'; else; 'no'; end
=> "no"
```

Therefore in ruby `if a and b` is fully equivalent to `if a && b`